I am working on this small project and I have houses on one blend file, and the main stage on another. When I modeled the houses, I modeled the roof and base of the house and door etc. all separately. When I textured the houses, I took a tileable texture (such as brick) and unwrapped the house walls. I do not have uv maps for the buildings, just single textures that the unwrapped walls are being stretched so the tiling effect would happen.

Now for my question. How would I be able to quickly and easily be able to create a map (so I can join the different parts of the building) without having to retexture everything?

I hope I made sense… :S

I think you mean baking textures, for each part to a single object.
I’m not quite sure how to achieve this particular example though.

I have tried creating another object and baking the textures but the textures are blurry and don’t even bake onto the object correctly.

For one thing, if each part of the house has a different material assigned to it, then all the materials should be there when you combine the parts into one object.

And it’s generally a prerequisite to have UVmaps for all textured objects in the BGE, as the generated and object texture coordinates are only partially supported when using GLSL and are only usable for planes.

So does that mean that I have to just retexture the whole thing? But this time create a uvgrid for it first?

In short, yes, but it’s a matter of creating a UVmap for each object and assigning the textures you have to use UVcoordinates instead of generated or object coordinates if you’re using Blender materials, and you will not have to fish around your hard-drive for your image files as they should already be selectable in the .blend file.