Getting started with DIY Subs

[Snpbond]

I'm looking at building my first DIY sub in a little while and wondered if anyone had any really good resources to help with the planning. There are a ton of great build threads and guides here and on AVSForum but it is a bit overwhelming as to where to start.

As to what I'm looking to build, either a 12" or 15" driver (may be getting a 15" from a friend to use) and am looking to hit sub 20Hz (tuned to around 15-16 would be great).

I guess I'm asking if there are any good designs that I could just use or if I should map everything out in WinISD and build a box off of that. Thanks for any help, I'll be sure to follow up when I actually start the build.