The Way
There are plenty of way to build a tube amplifier.
Tube Amplifier Kit
Basically, a tube amp kits is a full set tube of amp parts which come with tubes, components and chassis. This is the easiest way to build a tube amp. What you need to do is to assemble all the parts by following the instruction manual. You are free from a lot of headache likes drilling, cutting, filing, or maybe winding. Beside that your budget for the whole project are pretty under control.
Kit Module
Kits Module is a partially finish amp, it may be a complete amplifier circuit, power supply unit (PSU) or a small section of the circuit. Most of it come with printed circuit board (PCB) and components. Since it come with the PCB, wiring job and connection error is reduce to minimum. The only thing you have to prepare is the chassis. So drilling, cutting and filing may not be avoidable.
Cloning Reputable Tube Amp
Cloning a reputable tube amp is a more advance option for builder. Most of the time, a well known tube circuit design which is well acceptable by many builder (DIY-er). Some are from reputable brand/designer like Leak, Quad, Fisher, McIntosh, AudioNote, Dynaco, Marantz…etc. Cloning is not easy. You need to have at least basic understanding of how tube amp work, how to deal with wood or metal chassis. Beside that you need to know the components rating, specification, components building material, wiring and grounding topology. Lucky, some builder are kind enough to share all the building process and they even put up the Bill Of Material (BOM) for you to refer.
Zero to Hero
To design or redesign in order to improve a tube amp. This is for person who really dedicate them self to tube amplifier. They spend a lot of time doing all kind of testing, trial, and many year of experience to come out with a tube amp which fit certain purpose. Some of them even create a help desk in forum in order to help other to build tube amp. This is not a easy job. Plenty of question, some are well known and some are unknown, every question need time to answer. I really do salute for them.