Welcome to the forum!
If you have a small budget I would suggest building a control panel for a start, even if it is just a 1p panel.
That way you can practice your wood skills (if you need to) and you will learn plenty that you can apply to your full size cab. Once you have a functional CP you will find you will have plenty of time to save as you will be hooked playing games

If you are then happy that you still want to build a cab, great

As the guys said, this can be a very expensive hobby and the sky really is your limit. Even if you are building a simple cab its suprising how much things add up to. You don't want to cheap out no matter what spec cab you are making. The last thing you want to do is to make a cab and then 6 months down the line think 'if only I had put some extra £$£$ into this/that'.
Start saving money, research the subject, design your cabinet, redesign your cabinet (etc etc) and only start buying components/controls when you are 100% on your final design/spec. Its very easy to get excited in the beginning and buy a load of components/controls that you don't end up using.
Most of all have fun and good luck!
