The best method for building a drum room is a non-parrelled wall or trapazoidal room design, with dimensions of at least 10 X 12. The ceiling will probably be 8' (assuming it's in a residential area) but 9' or more is definitely better if it's a commercial space or new construction. There's two ways to approach a drum room. You can do it well, or do it cheaply. We'll start off with the "correct way"

• You should build a double studed wall or "room within a room" framework with 2X4 walls on rubber isolaters. There should be no wall to floor or floor to ceiling contact.  Use R-13 insulation with a double layer of 5/8" sheetrock on each side. This is put on all walls & the ceiling. You may also use resilient channel inside the room to further isolate the room.
• You should add provisions for a 12 to 16 channel XLR snake with 4 channels of 1/4" TRS. You can use a stage snake, and run it through the wall and seal it with non hardening rubber sealant. Another method would be to add patch panels on the wall, and run the wiring in conduit in the walls or floor. It's best to surface mount your electrical boxes so you don't put holes in your sound-proofed wall. During new construction, some people will buy 3" or 4" PVC and run conduits between the control room and drum room in the cement slab. This allows your snake to be consealed, and also upgraded or repaired.
• Two Solid doors opening away from each other should be used as an entry. Use 36" doors so the drummers don't have to struggle with the kick and floor tom.  The window should be 2 panes of Plexiglass 1/2" thick on an "A" angulation to prevent the buildup of standing waves. This method provides approximately 50-55 db isolation.
• This is a preference area: Cover the ceiling with acoustic tile, cover the walls with nice carpet.  Use hardwood flooring.

• Use single studded walls with R-13 insulation. Use 2 layers of 5/8" sheetrock on each side, covered with carpeting, and a tiled floor. The window is 1 thickness of 1/2" plexiglass on a slight angle. Use a single solid core door as entry. This will provide 30-35db isolation. This room can also be used also as vocal booth or amp room.