First, look for a good plywood stretcher.
That is a very good frame design, and with good tools, isn't that hard to make either. Good job! Did you use glue at all of the joints? I would always trust good quality glue more than screws, and with both, you have a indestructible frame.
Why don't you look for a pre-built door or doors for the front, then design the "skin" to go with the doors? Those doors aren't excessively expensive for what you get. The downside might be the difficulty of matching the canopy to the stand/doors.