I wondered if anybody's done this before. I've not downloaded too many custom worlds so forgive me if this is an old idea. In building my world and trying to get a" downtown" feeling I've thought about ways to add deco to fill out the empty spaces. Let's say, for example, you wanted to build a block of connected, downtown buildings and storefronts but you only have one or two playable lots on the block. Could you simply build the outer structures of the deco buildings onto your playable one and then put hidden room markers in them so sims don't go there and you can't see inside? I'm presuming outside the lot the structures you added on would still be visible but they would just be décor to fill in the space.

Any potential problems with this method? Has anyone done it?

It's very often done in city like worlds, They make highrises with or without cfe, sometimes they make stores on the ground floor and the rest is just hidden, You can use a skip floor marker as well on floors you don't want to see in game. The walls you can use some regular EA walls and cover them with shiny metal, and it looksl like windows on a distance.