On the detail side, such advice must be based on thorough practical knowledge of what it costs to man and clean a building, to maintain its elevators and heating and lighting plant. This involves knowledge of the pay roll of help of all sorts - superintendent, mechanics, engineers, janitors, scrubwomen, elevator men. Their number and kind are determined largely by the sort of service the building is to offer, and the kind of service is determined by the class of building. Repairs and upkeep must be figured to a nicety; coal and even oil consumption computed in advance. When buildings cost from 40 cents to $1 a square foot to maintain, it can readily be seen that all items which add wastefully to the cost of upkeep must be eliminated - that every possible square foot be used for offices. A maintenance cost of $1 may be all right in a building where rentals are $2.50 a square foot, but a cost of even 75 cents for maintenance would be a bad proposition in offices renting for $1 a foot. The experienced manager, therefore, endeavors to eliminate features that will run up even the cost of keeping halls clean. For example, certain brass work on the front of a building may require the entire attention of a single man and his wages must come out of the gross rent account.