The roof sits on the side walls they are what is called load bearing walls. The ends don't have nearly as much weight on them and that is where the door opening must go. It would be possible to reinforce the thing but that will be a lot of work and expense. If you could get by with a small walk through door that would be much easier to install.
My advice would be put the GH in another location or sell it and buy one designed like you need but nearly everything will have the door in the end not in a load bearing wall.
I own a 10x12 hfgh and I reinforced it just to get it to survive cutting out the side wall studs for a door would weaken it and it is already a flimsy built structure.

Thanks for the info, I don't have it yet, that was the buying decision. I really don't have another place it can go.