This Instructable shows you how to make a relatively simple pull-up bar that installs in the ceiling. Some other designs require mounting a bar to a 2x4 which is bolted across several joists or studs; with this method, you can just use two simple eye bolts to mount it directly to the joists.
Step 1: Materials
I got all the materials at the hardware store. It cost less than $30, which was cheaper than the wall or ceiling bars I found online. You will need:
1 36" length of 1" electrical conduit
4 3/8" quick links
2 3/8" S-hooks
2 3/8" x 4" eye bolts with nuts
2 3/8" x 4 1/2" eye bolts with screw threads
2 3/8" washers
3/8" and 5/16" drill bits
Make sure that the hardware you buy has a load rating appropriate for the amount of weight you'll be putting on the bar. The lowest rated part I used was the eye bolts, and they were rated for 160 lbs. With two of them, you should be covered under most reasonable use. All of the measurements and hardware sizes are adjustable - I just bought the heftiest looking parts I could find in the store. For the bar itself, I chose aluminum so that I could drill easily through it - at this length it was clearly strong enough to support weight without bending.