Is the DIY itch irresistible? You really like building stuff? Or are there budget restraints? IME, DIY doesn't save money, but it's often worth it to build something cool.
"I've got a driver, I want to build a box!" threads are perpetual favorites with the TB gang. Hang in there. There will be lots of questions and volumes of advice.
Lots of guys have killer DIY cabs with solid designs.
Here's my questions: Is this for bass or pedal steel? Big difference.
If you really want to DIY, and these are basically stage monitors, could they be wedge shaped?
Can the drummer just buy himself a powered monitor, and you send him a signal, or maybe just upgrade the stage monitor gear for everybody?
I'd look into in ears. Silent stages can really improve sound for small gigs. Individual monitor mixes, and the FOH doesn't have to fight with stage volume.
I totally get it if DIY beckons. I like building cabs.