The rails will be difficult to make. Rail rubber must be glued on at a very precise nose height and angle for correct rebound and eliminate jump. I would forego the noisy slow rattling ball return for nice drop pockets. The frame is easy. Just make it level, square, and heavy if you are not using real slate.
Level the frame in place before putting the top on. Bolt top to frame and check level both directions. Shim under legs with playing cards to fine tune. You can also shim between frame and top. If the table will be moved regularly or pushed around by kids, I would opt for screw in/out adjustable feet on the bottom of legs instead of shims.
Covering the rails and table with felt requires special knowledge and cutting techniques. You may find helpful videos on youtube.
Easily overlooked is the space requirement for a pool table. For an 8' standard size table the room size is a minimum of 13'6" x 17'. Any less than this and you will need a short cue for certain shots.