Say I have a building with windows, doors, stairs, some wall columns and so on.
Places that would not need collision based on what they are by or the player will not be able to get to them.
Ceiling - no collision needed, why calculate it.
Wall columns on walls - Wall has the needed collision, so why add it to the columns sitting there.
The actual roof of the building needs no collision unless you are planning on walking on it.
Window separate, as transparency works best on those objects,when they are not attached to any other mesh.
Door will be separate as you may want them to animate and need to be there own objects anyway.
Most everything will need poly collision (1) so you can walk around inside with out being blocked by collision.
Now you build this stuff around the 0,0,0 of the model program, and export each piece from there locations so you can assemble the building by inserting each piece from the same snap location in the editor.
I use 3ds max for modelling and animation and have been for 20 years.
For a single building approach I would use 4096 x 4096 and sometimes that is not big enough and I will need to split faces.
Polygon limit in GameGuru is 22000 polys for any single object, or GameGuru will omit anything over that limit.
Use the entity basic shader in GameGuru and only use textures for mapping in Blender. Direct x must have textured UV mapping and nothing procedural.If you use procedural textures, then you will need to bake them out.
_D for diffuse and opacity - DXT1 compression except when using opacity, then use DXT5 compression as it adds the alpha channel
_N for normal maps - DXT 1 compression
_S for specular - DXT1 compression
_i for emissive or glow -this is a black and white map, with white indicating what you want to glow. DXT1 compression
,png files can be used, but they are slow to decompress in the game engine. .DDs format has various compression that allow for different things and opacities and Alphas.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.