I bought one about 30 years ago and it's been wonderful. Problem is that it came from a small company based in Leicester but I know they relocated to Birmingham and don't recall their details .
Mine will take two cars side by side, it's got 4 upright posts at the open side (80x80mm (?) square tube) and the house side has got some Rawlbolt fixings to the wall, and the usual corrugated clear PVC roof. I think the sections across the roof may be 80 (or 100) x60mm rectangular tube. All the tubes are white plastic-coated. The guy delivered the whole lot on top of a Range Rover, all ready pre-drilled. I think the only problem we had putting it up was that he had supplied 6mm bolts and he drilled the holes in the Al to 6mm, and I think we found things easier if we gave ourselves a 'bit of slack' by drilling out to 7mm. The 4 uprights are in about 18" of concrete and there's no sign that it's ever moved a millimetre. I guess that sooner or later the PVC will need changing, but seems ok now.
Two of us erected the metal work (and concreting) over about 6-8 hours and then I put on the PVC by myself at my leisure (very tedious).