these are the blocks I refer to:

By pricing per flat, the owners have a fixed price and I have a good job.
If I were to price per window on each block, that would be:
Each flat has 4 small windows and 2 large windows:
small window: £1.00
Large window: £1.50
per flat would be £7.00 (that is what I charge top floor flats)
per block would be:
£1 per small window x 48 windows= £48.00
£1.50 per large windows x 24= £36.00
That would be £84.00 per block
My per flat pricing is £68.00 per block.
I could not do this cheaper or any slower. I do not go fast on these, they are just good WFP friendly windows all in one place.
All a flat owner knows is that they pay £5/£7 every 4 weeks to have their windows cleaned.