Its just a case of breaking up your level parts.
For example a simple room could be baked to one 1024x1024 texture, however it would probably be best to break them up into more parts. For example floor, walls, ceileng etc.
Another thing worth thinking about is for level geometry that is not moving, to use 'World' instead of 'Tangent' for your mapping. Essentially tangent works from the normal of a surface, so that if the surface rotates, the GPU can work out the new position, however if its not going to rotate, 'World' has a much better result. Certainly worth experimenting with.
So you should be able to follow the tutorial and use it for levels in the same way that you do models. The indiMECH is made up of about 6 parts, each with their own diffuse, normal & specular maps, which are then put together in engine. This is the same for levels etc.
Just as Drew has done above
Hope that helps