5 yards is probably close, I had purchased NOS material by the yard for a 71 Mercury cougar that I'm restoring. The car has a 1/2 roof and called for 3 yards. A Darrin calls for 7 yards for the top and side curtans.
Material is commonly sold in 54" wide to sew the top with the correct seams I would estimate 2-2 1/2 yards on the center section. then from the outer section which has to be long enough to cover from the A pilar back to the C pilar again will take between 2- 2 1/2 yards in length. The thing to remember is if you try to get by and then find you don't have enough your going to need to order another 2-3 yards.
The down side is there will be alot of waste because of the irregular shapes of the pieces needed.
