Wheelbuilding/truing - Every cyclist should have a go.
I did it for years using a frame or forks plus bits of tape and pencils for a wheel jig, then bought a cheap commercial jig that wasn't much better than the frame and forks etc. Recently bought this book:
http://www.wheelpro.co.uk/wheelbuilding/book.php
and made the jig and other tools described in it. I made them all from bits of wood etc. I had lying around, except for some bolts and wingnuts. The wooden jig is far better than the commercial one I had; easier to use and more stable.
The book is well worth the £9 or so it costs. It'll save you that in costs and inconvenience during your first couple of builds.