Level texturing

I’ve got this big ol’ level object I’ve spend a lot of time on. There are lots of smaller pieces (computers, beds, tables, boxes, what have you) but the bulk of the level is one large somewhat complex object. I need to figure out how to texture this object properly. I don’t want to just apply one texture to every wall, floor and ceiling but blender doesn’t seem to give me any other options unless I want to spend hours putting proper seams on the mesh then saving the unwrap image, opening in gimp, and using gimp to edit and move multiple textures around in one image so they fit over the corresponding parts of the unwrapped image, then importing the new image back into blender - all of which sounds like more work than I’ll be able to accomplish in my lifetime. Just for one level.

Surely there is a better way?

One thing I’ve done is select the whole level and do an “Unwrap>Cube Projection”. Then when you assign a material you’ll get perfect mapping. Then select the faces you want to be another material and assign one to them. No need to use Gimp at all.