I would suggest that if you were going to build a PCB tube guitar amp, you'll probably find that by the time you buy all the expesive transformers, tubes, speaker and cabinet, you've probably spent way more than the cost of an Ashton or Bugera cheap ass amp, not that I am promoting such an amp. And what you will end up with is something that may struggle to last 10 years with the heat that it will be subjected to and the problems you may have in servicing it, breaking pcb tracks/pads as you try to replace pots etc.
If you can, go down the line of Point-To-Point amps, which are so much easier to service, you can modify them to your hearts content and it will last a lifetime. Go PTP and there are lots of kits out there.
Michael