Been there, done that. I built about 25 custom awnings approx 16' x 20' for large electrical transformers. Becaues of the size I had to use strut channel for supports. The custom made canvas were quite expensive and had to be replaced about every 2 years. We had to install grommets around the entire perimeter to tie the awning to the frame. They are no longer in use because the transformers were too expensive to maintain and got taken out of service. I think the expense of fooling around with the custom awnings was what did it.

"How hard could it be to DIY?"

How hard are you trying to make it? Is your goal to save money, or just prove it can be done?

Is your tailor working for profit? It will be expensive to have something custom tailored.

What are you planning on for the frame? Electrical conduit, copper, PVC? Strut channel is really too heavy and the edges cut through the fabric. Do you really have the skill to build a metal frame that a taylored piece of fabric will slip over and fit snugly? Unless you have much experience at bending conduit or pipefitting, forget it.