The adventure of building something yourself is always a great one. You will likely learn a lot. Just be careful, make sure your solder joins are good, test along the way, power it up slowly with a varistor.
Basically, a decent kit will also have decent instructions. Read a few on-line articles on DIY tube amp building before you start to see what you are up against. Tube amps have high voltage, and can be dangerous. Can't emphasize that enough. But to me, DIY is a whole 'nother end to this hobby that many people don't explore, and it can be very rewarding.