I clean 2 polycarb bus shelters for a local parish council. Charge £45 each, twice a year. Clean inside and out, bit of tfr and pure water. Do them on a Sunday (no buses).
Submitted quote with risk assessment, method statement and copy of insurance to Parish clerk. Payment a little slow as has to go to council meeting to approve payment.
I know a trad firm in a local town does a few for £10 per clean, but I think that is monthly.