40 windows - if they are evenly divided between the 3 floors as you show then maybe....
40 divided by 3 = 13 roughly per floor.
If you're happy with £1 per window.
£13 bottoms.
£15 next floor
For third floor you need at least half as much again.
£13 + half = £7 = £20
£20 +£15 + (£13 - round up to £15) gets you £50 + "Commercial"@ £10 = £60
Where I am that's about as much as you can get away with I reckon but in Shakespeare country maybe more?