I built mine from scratch so that I could tweak the design to suit me personally. As long as you draft everything beforehand so that you can alter things as you go along. I found that it was a great way of really getting behind the skin of the internal workings and much cheaper than buying a kit. But that might be partly because I made some alterations to suit myself. I don't think I ever follow instructions.

I found that the most important thing is to make sure it's structurally sound. It makes the calibration so much easier.