My windows are double 36" width windows for a total width of 72".
Would you recommend making 2 36" shades or would a 72" shade work if the fabric is not heavy?
A 72" roman shade would be just fine.
It really has to do with your preference. If you really like the look of an extra wide roman shade, then you should make just that. Don't settle for 2 roman shades if that's not what you want.