Trying to Build a Modular on Your Own

I'm not an architect by far. I only build mechs, spaceships, and other vehicles. What's to stop me from building structures like those modular sets?To start, and make things as basic as possible, I went with rebuilding the set 67051 (Marvel Super Heroes Airport Battle set) into a fully covered structure. As it is, the only covered part is the front and sides, the rear's open. To make it sealed, as well as 'modular' I got another separate bag from 67051 from a seller containing the control tower (with the trolleys as a bonus).I extended the rear to allow for a rear wall, extended the heigh some more since I have extra wall pieces. I made the walls removable by adding aditional plating to the original walls and added a 1x8 tile for the rear wall making it removable. The top floor panoramic windows is just the same build of windows coming from the 2nd tower I bought. The extra antennae and other objects, I've added to the roof making it busier/more detailed.The build can now be used in my planned airbase diorama.