Room hire charges

How much do you charge for hire of rooms? We have a new building being built and we will be refurbishing our current premises. The rooms will be available for church and community use, Can anyone give me an idea on how much we should charge for hire of rooms? Do you base it on the square metreage? Does anyone hire their rooms out to an independent Pre-school and if so how much do you charge them? Thank you! Pauline Griffiths