I'm new to this forum, and I wish I had found it sooner as it seems great (and it would have helped me make a few less mistakes in my journey)!
I'm an acoustic engineer by trade (note not sound engineer) and thought it therefore necessary to delve into creating a cab at some point. So I started with a 12" sub driver I've had for a long time which is housed in a car sub enclosure. Packs quite the punch at low frequencies as it's meant to sit in your car boot...but severely lacks at mid/high frequencies (cut off is probably around 400 Hz or something).
I tried it for a little while and even took it to the practice studio, and it could hold it's own but it lacked any sort of clarity. I therefore decided to bolt an extra driver on top to help lighten it up. Standard ply box very crudely cut to size, with all the mistakes hidden by a nice piece of felt to finish. I added an 8" driver, stuck a crossover network in and hey presto - I ended up with something which covers a lot more of the spectrum now. Thankfully I want to uni with someone who works in loudspeaker design and they were happy to help design the crossover network.
The second picture is me trying to measure the frequency response - worth noting that I don't own a mic stand or a mic of any quality hence the rather strange measurement setup.
All in it's probably taken me 3 months to do it although it's felt a lot longer! As I'm not in anyway a pro musician I couldn't justify big spends - I think the top cab cost just over £100 inc the driver, ply and crossover parts.