Blender and Unity modular City

Hi everyone!
Here’s my question/problem:
I’m planning to do a modular city enviroment, but now I’m not sure how to handle it best… while setting up the uvs and textures for some props I started to ask myself if I should do every seperat modular piece with a extra texturemap (this would be quiet a lot… and that’s not a good thing I guess…) but if I put more modular pieces into one object to set up a propper UVmap and texturemap (with more than one piece on it) will it be possible to duplicat a specific piece out of the object within unity? (I still need to get into unity, which I didn’t touch till now…)

For example, if I’d build a house, made out of diffrent pieces like seperat walls, stair, windows, roof and so one, all within one object and all sharing one texture map, would it be possible to use the roof for a diffrent house, which would mean that I’d need to make an instance of only the roof, not of the complete house.

Sorry, if the question is stupid. As I said, I still need to get into unity, and don’t worry, I’m not planning to do a game, it’s just an enviroment piece (for my portfolio).

Anyway, thanks!