The above by Mindgap are very good.
I have experience with the Opera kits from www.diyhifisupply.com and www.diycable.com and can recommend them.
Both are very good for the money with lots of support online. There are a lot of modifications that can be done. Each has an online forum so you get a lot of help. A key question is how much power do you need, that is, what speakers are you using. The Bottlehead power stops at a 300b.
The Audio Asylum diy tube section is very helpful too if you have questions.
If you are just starting out I have a long list of online tube info you might find helpful. Drop me an e-mail I'll send it to you.