If the building has a total of 112 windows (60 + 52) and
you want 50p per window that makes for 66 quid, or are there
more windows ?.
If you think your price is too high, then try to estimate how long
the clean would take you and multiply it by your hourly rate, add
25% for profits and risk of false calculation and make em a quote.
If there are 16 apartments then they will be eventually paying for your work, £560,.. through 16 apps. would mean to each tennant £35,..minimium per month. cant see them forking out that much, but 112 windows x 50p + 25% = £70 divided through 16 tennants would cost them each £4.38 they would jump at that.