For the NEW price of a mid-level cab; if you have good woodworking skills and tools already, you can usually do as well or better than what most of the big brands offer. You need to either follow a proven design or use software to model your own, though.
If you need much in the way of tools to complete a project, or dont have decent kung fu with bulding from wood, IMO either expect less-than-stellar results or just buy a cab.
If you're really good with building, have a shop, and are willing to prototype first and take a loss (or two), a few hundred bucks can get you a better-performing cab than what that same money can buy you in a manufactured product new.
Most entry-level cabs are actually more reliant on the design than the driver itself. The off-the-shelf Eminence and Faital drivers are typically better drivers than the low-end lines use. Following suggested box designs for these drivers, you probably will get better results than an inexpensive big-brand offering.
Dont expect to save a significant amount of money though, once you add up the little details. You're paying retail prices for the small stuff; and it really adds up... Handles, corner protection, connectors, connector plates, grill material, finishing material, feet, and the fasteners to put all that stuff on can add 50 or (probably) more bucks to the cost of the drivers and wood. That still doesnt account for your time, adhesive, sand paper, consumables like shop rags, drill bits and saw blades, waste like wood scrap, wood fill that you sand off, stripped screws or solder blobs, overspray or cut waste when you tolex, on and on.
I absolutely encourage anyone who is a tinkerer by nature to just dive in and go for it, though my words above may hint towards discouragement. Just understand rolling your own is not a way to save money; if that's the goal, just shop used and be ready to pull the trigger on a hot deal.
Good luck!