Hadishon:
I don't charge by the square foot, because every roof is different. Some are steeper, some have a lot of gutters, some have no gutters, some are just square buildings, and some are fairly complicated. Basically, I look at the job and do my best to determine how long it should take....Take my hourly rate and you've got your price!
Two ways you can approach condos. First, contact the board members. Depending on where you are, getting that info may or may not be easy. Here in FL, it is easy, since the condo is a non-profit corp, and the corporate officers of all corps are available online. All you need is the legal name of the condo assoc. and you can get the board member names and addresses.
Second, you find out who manages the association, and contact the manangement company. That can often be difficult, as far as getting people to take notice. What you need to do is find out who the decision maker is for that property, and either get them on the phone or get them to agree to meet with you for a few minutes. Bring pics and a proposal, and you never know what might happen. I can say this...cleaning condos is great...You are there for sometimes several days, so the money is pretty good.
I don't have to work too hard getting that business, since I am also the VP of the largest HOA management company in our area.