rolande replied:

G'Day Lenni,

Our local canvas man was asked to do the same thing.

His first answer was to just purchase one from a good supplier, as they were so difficult to get right the first time it would not be worth his while attempting it.

Cavalier and Southern Cross in Victoria both have good quality kits.

You may find this much easier, (and cheaper), in the long run than trying to make something as a one-off

Hope this helps

Rolande