multi-texturing an object

i made a basic hall that took awhile to subdivide and combine faces… here’s what im at

i left open areas for the doors, but how do i texture the roof, walls, and floor when its one object?

You need to set up multiple Materials. Textures come under the umbrella of Materials. Look out for tutorials about Multiple Materials on one mesh. These tutorials will show you how to assign groups of vertices to particular Materials. You can have up to 16 Materials on one mesh.