Low, loud, small. You can have any two you want.
You say "Indoor arenas." How many people are we talking about? What type of music? The type of music typically dictates what volume levels we're talking about.
I do some DJ work and live sound reinforcement. I built an all-BFM system. Four T48s and four OTop 12's, all with the premium driver. It's more than enough rig for 300+ people indoors and I run the whole thing off two amps. If you're looking for a PA system, I highly recommend the BFM forums. Some folks here (like me) have experience with DIY PA cabs, but most don't as this is a home-theater oriented website. The goals and usage of PA cabs is very different than HT cabs, especially in the subwoofer department. Example: My T48s will play down to 30Hz but it's safer to HP them at 35Hz, which is what I do. 35Hz is laughable for a HT subwoofer. You'll get more of the type of help you need over at the BFM forums.
That said, looks are nice but it's the performance you should be concerned about. What sort of DIY skills do you have, by the way? Have you ever built a speaker cabinet before? BFM cabs offer superior performance to any commercially-bought cab costing 2x as much or more, but they are much more than a simple box to build
Last edited by michaelddd; 01-15-2016 at 03:37 PM.