I have a building that I am going to clean that is 3000 sq ft and I want to charge $.15 a sq ft. I did this, 15*3000 and came up with $450, but the client mentioned the last quote he got for the same sq ft was $4500, so am I calculating it wrong?

15 cents per square foot times 3000 square feet is, indeed, $450.

To me, $450 sounds like it might be a bit low, but $4500 is WAY WAY too high.

Tell us more about the job and we can help further.
Is it residential or commercial?
Is it one unit (a house) or is it a building of multiple units?
Is the building occupied?
Is this just a one shot deal, or are you talking about doing it once a week or once a month or once at some other interval?

Do you have specifications Katherine? It sounds to me like you may not be totally informed as to exactly what they want done.

Is this an on-going job or a construction clean up?

Even though I too agree that $4,500.00 seems very high for only 3,000 sq ft there could be a lot of other work involved; ceiling cleaning, wall cleaning, window cleaning (acid?), carpet cleaning, VCT / hard floor stripping and refinishing, bright work cleaning, mold cleaning, terminal cleaning if a medical facility, etc.

Do you see where I am going with this? I would again ask "what exactly is to be done?"

Stringer