+1 on the 8ft, I've seen 6ft on the 16 foot boats and they look dinky and don't cover the rower and the passengers at the same time. I put a 8ft on my 14 foot boat and it is perfect.
If you want to make your own, you can buy all the fittings needed at most boat supply places that sell biminis or search for "bimini hardware" and enjoy... I bought mine at Sportsman's Warehouse. I think I cost around $350 for the attwood frame and sunbrella fabric top. Not cheap, but totally worth it.