LEGO MOC Design Creation Process Guide

Reading Time: 7 Min
By Kim
Published: 20 January, 2021
Updated: February 7, 2023
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Like most LEGO® fans, when I started with the hobby of rebuilding LEGO® sets into my own creations (MOCS), it was mostly impulsive; grabbing the pieces and playing around trying to create a certain look. I neither had a plan nor a target finished product.

As I learned more about MOCs through videos, articles, social media posts, etc. I’ve realized that there is more than just one type of MOC. Although it’s not official, I’ve categorized my MOCs into three; 1) modification, 2) original design and 3) alternate build.

Modification is taking an existing official set and adding parts to it and enhancing its overall look and/or function without totally deviating from its original design. An example of it is the modular privet drive which was inspired by the official set 75968.

The MOC still reflected the overall look and purpose of the set but had a complete layout and function of a modular building. The advantage of this type of MOC is that there is already a base set to work on.

The designer only needs to improve by adding parts to it and making it look & function better than the original. The disadvantage to modification is its tendency to look very similar to other MOCs created by other designers; therefore, compared to other variations of the MOCs, it does not stand out as much.

lego moc creation process image 1

The second type is the original design. It can be based on real life buildings or purely from imagination. Its aesthetics and/or function does not come from any official LEGO® set. The whole concept comes from the designer.

The advantage of this type of MOC is its unique look and function. It stands out among other official sets as it is not commonly seen by LEGO® fans on LEGO® boxes or from other designers’ MOCs.

The creator also has an unlimited range of options with existing LEGO® parts during the design phase. The disadvantage of it is that the creator starts from zero and work their way up until it is completed. During the actual build, collecting the parts can also prove to be harder since they do not all come from just 1 or 2 official sets.

A sample of this is the Seamstress’ shop. It does not look like any official set and as of writing this article, the type of business on its ground floor has not been showcased by LEGO® on any of its modular themed buildings.

lego moc creation process image 2

The third type of MOC is the alternate build. It is somewhat a combination of the first two type; but takes on both their advantages and disadvantages.

The alternate build is when only one official LEGO® set is used to design and create a structure that is different from the original look and function of the official LEGO® set. The advantage of this type of MOC is the relative ease to collect the pieces required to build it as well as its unique look compared to a modification.

The disadvantage of this type is the limitation on the parts that a designer can use. A sample of this type is the Birch Art & Antique Corner. All the parts come from set 10270 but the overall look and function of the building is different from the official design.

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Among all three type of MOC’s, the alternative build is considered the hardest to do due to its limitations on the accessibility of parts. However, this disadvantage can be turned into an advantage if enough thought process and preparation are done.

As I developed my skills and techniques with MOC’ing, I’ve come to set up steps and guidelines to help me through the process. These steps and guidelines improved my efficiency and creativity in creating unique MOC’s.

Some creators choose to design digitally or in actual. Others choose to do both. The steps and guidelines below are directed at helping creators and designers streamline their digital and actual MOC process when doing alternate builds of modular buildings.

The reader may also apply some of the techniques to modifications and original builds, when possible.

Pre-design Phase

During the pre-design phase, the designer has to choose an official set as the basis for the MOC. The quantity and quality of parts in a specific set have to be considered. 3-in-1 sets have the potential; however, due to the low quantity of parts, they often require 2 or more sets to be able to create a modular building.

They then fall under the category of modification rather than alternate build. The most common themes to be used in alternate builds are the modular buildings. The provide enough quantity and quality parts to give the designer a basis for the design.

After choosing the set to work on, the designer can then look at the available parts in more details. Special pieces like large panels, modified bricks & plates and irregular shaped parts should be prioritized when coming up with the design.

These pieces can and usually will define the overall aesthetics and/or function of the alternate build. An example for this case is the use of curved & straight panels of the downtown diner.

The original set had the on a normal position which defined the look of the building and set it apart from the other modular sets. The alternate build took it a step further by turning it vertically and using it as somewhat of a skylight which is not usually done by designers.

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The next step would be to choose what type of establishment or business the designer intends to put on the building. The designer may choose to opt for one or more businesses considering the availability of parts in the set.

The alternate build can become a totally new type of business like Birch the Art & Antique Corner. It can also be like Jim’s Bowling Alley which complements and serves as an extension of the original set.

Design and Creation Phase

After choosing the type of establishment, the designer can import the parts of the specific set and commence with the digital work. The focus remains on the special pieces of the set to establish a general theme for the building and from there, work outwards. During the design of the Birch Art & Antique Shop, the focus of the build was on the spiral stair case. After placing it at the center, the layout of the building was then created in a way that would be able to showcase it even from an exterior point of view. Though the original bookshop made good use of the spiral stair case, it was only visible when the modular was opened. In this MOC, it became one of the focal points that connected two different establishments.

lego moc creation process image 5

The next step is to build the bulk structure of the building using the basic bricks, doors and windows from the ground floor going up. During this step, it is advisable to create multiple copies of the structure as it can become a “trial & error” scenario.

Given that the designer is working with a limited number of bricks, windows and doors, careful placement of bricks and sizing of building is essential to ensure that enough pieces are available to complete it.

It also runs the risk of not using enough parts; therefore, leaving a lot of spares at the end of the MOC. During this step, the designer may look into the original design to gauge the achievable size of the MOC.

It is for the same reason that the Privet drive can only be modified into a modular style building and not an alternate build. There are just not enough pieces on the set for it to be possible.

After digitally working on the main structure of the MOC, the designer may opt to start working on an actual build. There are designers that build purely on a digital software; however, there are those like me, who prefer to do both.

Actual builds tend to become a way to check the stability, integrity and constructability of the design. The designer can see potential problems during the actual build that may not be apparent in the digital design such as clashes and overall strength of the structure.

At this point, designing & building digitally and in actual becomes a cycle. One complementing and quality checking the other. This further helps during the preparation of instructions since the designer can better visualize the procedure having done the build in actual.

After the main structure has been built, the exterior aesthetics come next. Using the remaining parts, the designer can add details to improve the exterior of the building. Modified bricks, plates and other smaller pieces can be used as greebles to enhance the look of the exterior and create more texture & depth.

However, the designer also has to strike a balance with the use of greebles to avoid having the building look cluttered. It’s worth noting that at this phase, it’s best to experiment with the different aesthetics digitally before doing it on actual.

lego moc creation process image 6

With the remaining parts of the set, the designer can proceed with the interior. Using small builds inspired from the original set will make it easier to fill the interior but like everything else, the designer can choose to create furniture and appliances using his own techniques.

As shown in the interior of Jim’s Bowling Alley & Diner, the car that came with the official set was split in half and repurposed as an arcade game and an in-door movie seat.

lego moc creation process image 7

Completion Phase

Once the MOC is almost complete, the designer may then go through the design several more times and incorporate the remaining parts that have not been used.

The designer may take a break for a few hours or maybe even a day so they may look at the MOC with fresh eyes. There are details that can be added which may not have been thought of during the initial completion of the MOC.

Post Completion Phase

After the design and actual build have been finalized, the designer may choose to create instructions or render 3D photos. If the instructions are prepared and generated as PDF, the designer can go through the steps and perform quality check to ensure that the instructions follow a logical sequence.

lego moc creation process image 8

All designers and creators have different styles of building MOCs. Some choose to only build in actual, some only do digital designs and some do both at the same time.

As a reader, you may choose to follow all/some/none of these steps and guidelines as long as it suits your preference.

The important thing to keep in mind is to try to continue learning and improving. Most of us do not have an unlimited supply of LEGO® parts. What we do have is an unlimited imagination. If we use it properly, we can build anything we want.

Do what you can with what you have. Innovate.

Let us know what you think by dropping a comment below!

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Hey, I am Matthew Mitchell and I am an AFOL from the UK. I have been fascinated by LEGO since I was a child. My two children are in love with LEGO and it's because of them that my interest in LEGO continued to grow, this is how I fell in to the rabbit hole of LEGO MOCs. 

With every new LEGO MOC I saw I became just a bit more addicted to the endless possibilities that LEGO offers. This led me to creating Belle-Ve Bricks, a platform where talented LEGO designers can share their work with the world.
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