A veranda as a kit is deliberately designed so two people can put it up. What people underestimate is not the assembly, but what comes before it.
The ground determines the result
If the foundation is not level, you see it back in every profile that goes on it. Posts lean, roof sheets do not close up neatly and sliding walls bind. Measure the ground before anything arrives and correct it then, not afterwards.
Measure the wall, not the drawing
House walls are rarely entirely straight and floor levels slope. Measure at several points and work with the actual dimensions. It is the most common reason an order does not fit.
Do not do it alone
Roof sheets and glass are awkwardly sized and breakable. Two people is not a luxury but a requirement, and with glass rather three. A broken sheet costs more than an afternoon’s help.
Lay out your tools beforehand
A spirit level of at least a metre, tape measure, cordless drill, combination spanners, ladder and caulking gun. Stopping halfway to fetch something is exactly the moment things end up out of true.
Do not work in the wind
A roof sheet catches wind like a sail. Pick a calm day; it saves material and irritation.
When to hand it over
With a large span, working at height, or when the structure has to be fixed to an existing extension, professional installation is worth considering. Also if you simply do not fancy giving up two days off — that is a perfectly legitimate reason.