Since I'm also in the process of researching DIY screens, I can tell you what I'm doing - using both left and right arms - since you are the one who got me into this whole HT racket, I am probably just regurgitating stuff you already know, so be prepared to have your time wasted:
The gist is this - start with the screen gain you need, then look for material/paint to achieve that gain.
I'm trying to figure out what sort of gain I need from my screen. Brightness is measured in fL (foot-Lambert, obviously created by some poor sap named Lambert who was afflicted with super pale feet). Reading various things about screens, there's a range that is considered "ideal" for fL - that seems to be 12 fL to 16 fL for a fully darkened room. Obviously with ambient light more brightness is going to be desired. And bulbs dim over time so being able to go brighter than the ideal means you'll be able to still be in the ideal range after said dimming occurs.
I'm using the calculator here: http://www.eliteprojectorcalculator.com/
and that's one of the places I've seen that ideal fL range, FWIW.
After locking in on the projector model you have with that calculator, and then adjusting for the distance from the projector to the screen, you can then adjust the screen gain (very top of the calculator ABOVE the screen size slider control). Look at the left side of the calculator to see the fL for the various settings of the projector. Green means it's in that ideal range for a given brightness setting.
Once you know what screen gain you need to achieve your desired fL levels, then search for material that achieves that gain - at least that will help narrow your search down, hopefully!
GEAUX TIGERS! I'll be in the Dome tonight... I'll try to figure out what the fL is from the Jumbotrons.