My roommate and I bought a hangboard (aka a fingerboard) (the Metolius Project) from our local climbing gym (Planet Rock) about three weeks ago. We're both engineers, and so we decided to design and build a frame to hang the board from. Here's the result:
You can see that the board is simply supported by two A-frames, kept the correct distance apart by two cross members. They're simply built from 2x4's (which I learned actually have a 1.5x3.5" cross section). We had a fun time loading those on a shopping cart to transport them from the hardware store to the apartment. The wider board is a 2x8 (1.5x9.25" cross section). The vertical member of the board is 6 feet long, which puts the hangboard at an excellent height. The base of that triangle is about 42" long, and extends another 30" out for balance. The two A-frames are 42" apart from each other, measured from the inside. The extra space is so we can mount holds on either side, to practice on other holds (for example, vertical pinches).
The construction of the thing took maybe 12 hours in total, spread over three days of spare time (I think). The most annoying part was cutting the angles in the hypotenuse. The angles were cut by hand, which made their tolerance rather loose. We had to sand down the edge quite a bit. The holes shown below were done without any guide to make sure they're perpendicular, but it all worked out in the end.
This is the part of the rig I'm most proud of. The idea is to let the hangboard rotate, so we can practice steeper crimps. The original idea is to move the entire A-frame, locking it in with notches on the base. That would have been a construction nightmare, however, so we came up with this system where just the board rotates. Those holes are 6.25" from the pivot, and there's seven of them going a full 90 degrees.
This is the side of the pivoting mechanism. The center board is held in place by 4 bolts, and the side board is held to the frame by 6 screws each. This view also shows the extra board in the back, which stops the A-frames collapsing sideways. Mounting this board high up keeps it out of the way as we do pull ups, but there's another practical reason. Since the center board is only held by bolts, we can easily take it out and replace it with something else. In particular, if we decide to make a campus board later on, it can use the same holes for tilt, and can extend beyond the A-frame.
We still have a little work to do on it, the most important of which is adding diagonal beams between the frames to stabilize it further. There are also other things like sanding down the corners, clipping some screws on the back of the board, getting a pad underneath, and applying a layer of varnish. The frame right now is fully functional though, and it holds our weight quite well. Although I haven't looked at how other people mount their hangboards (usually just above a doorway, probably), I feel that this is probably the most flexible design you'll find. The flexibility with the angles and the modular design means it can function as a very general purpose climbing trainer.
We intend to have blueprints of the entire thing online eventually, when we're bored enough to play around in a CAD program. If you want to build one in the mean time, feel free to leave a comment and we'll help you out as best we can.