I've built my own cab and mentioned it in dispatches here some time ago.
It's a large, open back, sloped, 1x10. And it sounds fine. However, if your motive is to save money, I would suggest caution. It can work out more expensive than you might think. A lot depends on how professional you want it to look.
Before committing yourself, draw some plans and start pricing things up. Pop a tape measure in your pocket and go to your local guitar shop to measure a suitable 2x12. Measurements aren't that critical, an inch or two in any dimension won't make a great deal of difference. Then work out how you will build it and how much wood you need. Then you'll need handles, an input socket, feet, grill cloth, covering or paint... it all adds up.
If money is tight, hit the second hand market and find a cheap Marshall or similar. That will always be cheaper than building your own unless you happen to have speakers and parts to hand for free.
If you want to do it for fun or satisfaction, go for it. I can recommend it to anyone, but it's not a cheap option.
When the going gets weird, the Weird turn Pro.