If I were replacing a pop top, I would go for a high-quality fabric such as one of those used for boat dodgers and biminis (awnings). I say that because, like paint
, the cost of materials is usually but a fraction of the cost (or effort if you are using your own time) for the job. A good top will last a long time. Also, you are not talking about a large amount of yardage.
Things to consider are not only water resistance, but the ability of the fabric to withstand repeated "hinging" as you raise and lower the top, plus long-term storage when the top is down, abrasion, UV-resistance, etc. Some coatings stand up to that better than others.
Sailrite is a great, family-owned company that has a large variety of appropriate fabric choices, plus the clear window plastic, and etc. They also have a wonderful paper catalog that is packed with info, and they provide fantastic customer-service over the phone and will be happy to discuss the merits and weak points of any fabric choice.
PS: Does anyone else remember when tents were just "good old" canvas? Even though it was not waterproof, the walls actually were waterproof until or unless you touched them (from inside) while it was raining. I guess that changed the surface tension.