how to get nice building overlay textures

okey what im looking for is a way to do the extra detail on objects mainly buildings, so at the moment i will so many different types of textures for buildings, all being plain with no real detail to them.

what i want to be able to do is add an image over the top but a lot smaller image and many of them in some cases, so if you imagine i have a plain building, and on the side i want some graffiti, at the bottom i want a bit of grass, on the other side i have some vines running up the side of the building with moss spreading over the wall.

so how do take small images of these and apply them to a building but not add any more textures or draw calls.

by the way at the moment i use lights for graffiti and some other things and then bake it, is there a method similar to this or do i have to create my own

You could use the second UV set to map a second material with the details, but AFAIK then you lose the ability to do light apps on those buildings. So why don’t you just create planes in Maya that are part of the building mesh, and map the second detail texture to those planes? You’ll get more draw calls and you need a second (shared) material, but there’s no way around that anyway.