You assess the extra construction costs associated with the choice of site versus the expected longer term cost benefits of the choice of site.How do you do a cost benefit analysis of a children's hospital? Would you try and estimate mortality rates between building or not building? They do this kind of analysis when deciding whether to fund expensive drugs and it causes no end of grief for patients. The idea that you can estimate the cost of a new hospital on a cost/square metre is daft. It may be reasonable for a budget estimate but a budget estimate needs a large +/- 30% uncertainty attached. Note that the uncertainty in an estimate is not the same as a project contingency.