Those factory tents are ok, if you have a factory tear.
I am at the finishing stages of building a rather individual project, going through a fair amount of money and an inordinate amount of time in the process. Putting an import "cabana" beside it doesn't fit my schedule. !
There are pictures around of some very nice, obviously shop built side tents. I forgot all I knew about sewing, but I'll bet I can learn again.
It looks like one could be "framed" with copper pipe, or EMT or even PVC and a simple tent built to cover that frame. I've tent camped in enough wind that I'd make sure it was strong and attatched firmly to the tear.