Just a bit of caution... Vinyl isnt my first choice either but there is a reason why most all are made of it..... All bikini tops will flap in the wind, any "woven" materials will wear much faster at the friction and contact points. Also, if it is left out in the rain, water will "bucket" and stretch the top. All in all, vinyl will last much longer and is cheaper than a good top made of sunbrella (or its equivalent).
Other than that, they are simple to make and canvas-type materials opens up all kinds of possibilities of color.
Good luck!