Whether it’s multiple rooms or not, it doesn’t provide any benefit–each modular part increases the draw call count, and the lighting will have slight variations between meshes since it is processed on each object on a different thread. You can combine the modular parts using Blueprints, but that’s a hassle and still won’t be as efficient as just making a unique mesh the size you need since the modular parts would use more polygons than necessary. Also, if you use blocks then your walls will have to line up with those blocks otherwise you will get light bleeding when they go past the walls. The only issue, as I said is that if you don’t have enough detail in your lightmap at a high resolution then you have to split it up.