NO NO NO!! Don't canvass commercial like this, its cheap, tacky and the results are about ZERO
OK, this is how you do it.
1) Call into the reception of the company and ask for a compliment slip with the name of the person responsible for organising the window cleaning.
2) Send them a personal letter, short, to the point explaining what your offering.
3) Inform them you will contact them in a few days to see if you may be of assistance.
4) Contact them by telephone, ask if they need you, if no ask if you may call again in 6 months to see if circumstances have changed and diary the next call.
This is professional, approachable and gets results.
Think of it this way, how many emails that suddenly appear in your in box do you contact. Even if you were interested, you would be scared to open the email in case of viruses etc.......