The only bandpass worth building is the
DeathBox, because it's virtually impossible to mess up. The only downside is you need a good sized trunk to fit it in, and a pretty big passenger compartment to get decent SPL. I had a dbk12 loaded with a pair of JL 12w3-D2s in my old coupe, and it was insane-- 137dB
at 8 ohms... The box was enormous, though.
The Dbk for 10s is more moderate, but the box sounds decidedly better in the house than in the car-- I have a pair of them with Klipsch KV1089s in my living room-- they'll push 120dB+ on 50w each...
If this is one of your first experiences box-building, I always recommend sealed. The only foolproof box you can build. Ported is almost as easy to foul up as bandpass-- only when you botch the latter, it just sounds crappy-- and when you botch the former, you kill the speakers.