Hi timangiel
I can't answer your post/question exactly.... but I just wanted to share a little bit about what I learned having just bought a boat with a bimini.
It's a love hate relationship. For me.. there is nothing more frustrating than looking up and not being able to see my sails from the helm, except through a small little window... ghrrrrrr
The other problem is mine isn't easily "collapsable" (is that a word?) so when I go out racing I have to unzip and remove and un-screw... it's like a 10min process to break down and a 20 min to re-set up. (Tools, small screws and everything... holy crap!)
However, I can't imagine sitting in the sun now in the summer without one. It saves the skin on the top of my head! Very...very nice...
So.. If I were to order one custom made I'd get a big window in the top with a flap that covers it. ....and.... one that has thumb screws and is designed to fold up.
As far as "who" ....I'd start with a phone call to North Sails...but again, I'm sure there will be *way* more (and probably better) recommendations than that from our super-informative membership here on SN.
North probably doesn't make the frame and such.. but I'm sure they could recommend someone...
Hope that at least gives you a little bit of help...