Aluminium does not rust and glass does not wear, so a veranda is low-maintenance. Maintenance-free is something else. With a few jobs a year the whole thing keeps looking good for years.
Twice a year: the gutter
Leaves and moss in the gutter are the most common cause of overflowing water. Clearing it out in autumn and again in spring usually does the job. While you are there, check the downpipe is clear.
The roof
Lukewarm water, a soft brush and a mild soap. What you must not do is take a pressure washer to polycarbonate: the coating gets damaged and the sheet then yellows faster. Avoid abrasives and aggressive cleaners for the same reason.
Profiles and glass
The aluminium profiles need no more than soapy water. For glass an ordinary window cleaner works fine. If rainwater has left limescale, a vinegar-based cleaner helps — as long as you do not leave it on the rubbers.
Sliding walls
If a sliding wall runs heavier than usual, look in the tracks first. Usually there is sand or leaves in them and a vacuum sorts it. A silicone spray on the tracks works well; oil does not, because dust sticks to it.
Once a year: a quick check
Check that the fixings are still tight and that the sealant along the wall is intact. Sealant is the part that ages first, and replacing it is an hour’s work. A leak left over a winter costs considerably more.