I just simply work out how long the job will take, whats needed to complete it, how many people are needed, how payment is made (waiting times etc), any issues you may encounter on the job and then you set a price your happy with.
Depending on what commercial premises it is doing insides is different to cleaning a house as you can have desks in the way with people working on them, cabinets , book shelves, electrical equipment and so on, so you really can only look at the job yourself and work it out how long it could take, there is no magic formula. With a house you may have to work around a sofa and some picture frames and thats about it.