I wouldn't recommend the Torres kits.
I had one that Nick Guppy (guitarist) built for review. Texas something.
It was worse than shite.....a £200 Laney LC15 sounds better! ANd according to Nick it sounded worse before he tweaked some cap values....
Webervst makes good chassis parts, transformers and bits. Also Tube Amp Doctor make some kits, I've heard better things about these kits. Matamp can make you a box to put it in.
Another option is to try and get a production valve amp, gut it and install a Hoffman or Thundertweak circuit board, that's what I did as my first project. It's much easier than a total scratch build!