Draw a 2-inch square in the center of a sheet of graph paper. Draw four more 2-inch squares around the center square, one on each side. The finished product will look like a plus (+) sign. You will use this graphic for recording measurements. The center square represents the floor, the other squares the walls. Don't worry about scale; this is just a space to write numbers.
Measure your space. Whether a family room, spare bedroom or open basement, you'll need to know how much space you're working with. Three-quarters of your theater room's floor area will be devoted to seating and will require the most construction. Stadium seating (a set of raised stair-step platforms) is best because it gives everyone a straight shot at the screen.
You will need to know the dimensions of each wall--height and width. Mark down your measurements in the appropriate squares on your graph paper.
Draw out your room's floor space to scale on a second sheet of graph paper using one graph segment to represent each foot. You won't need to draw the walls.
Indicate any entries (doors). Don't worry about windows since they will be covered over. Now sit down and think. Just for illustration purposes, let's say your room is 10 feet by 14 feet (10 by 14) with the door along one side of a 14-foot wall 2 feet from one end.
The logical wall for your screen is the 10-foot one closest from the door. Write the word "Screen" along that wall.
Count four squares into the center from your back wall--the one furthest from the screen. Mark a line parallel with the back wall from side wall to side wall. (In our model this will be a 4 by 10 rectangle.) This space represents your back riser--the highest seating platform.
Four spaces in front of that mark another line from side wall to side wall. This is your second level riser. If your room were longer, you might draw another riser. Here your third level of seating will be on the floor leaving walk space. Note: Each rise should be about 1 foot above the other.
Now you can plan the amount of wood that will be required and think about what carpet you will want to use in covering the risers and floor space.
While you're in think mode, dream about the drapes for the walls--all of them, floor to ceiling. Heavy dark colors work best (most people prefer black or red).
Go shopping. You'll need the drapery material along with curtain rods and valances; the wood for construction (usually 1/2-inch ply and 2-by-6 studs); the carpet; and, of course, the recliners.
If you haven't bought your multimedia system, you'll want to consider the wattage for your 7.1 surround-sound and whether you want a plasma/LED screen or projection system. But that is for another article.
What you now have is a basic design that meets the minimal needs of a home theater space. You can also consider custom lighting choices, decor and trim. More elaborate theme ideas are available on the Internet.