How to calculate fees when Outsourcing?

Hi,
I'm an Architect that (like most of the architects in Ireland) have suffered big time with the crisis.
Due to there is now 9 month since I left my last office and wasn't been able to find any job within my profession (apart from few nixers here and there) I started thinking in the possibility of offering my profesional skills as an Outsource to architectural offices mainly. It's well known that many offices doesn't want to take the risk in contracting more staff,that's why and so far I cannot get any job so maybe offering them the chance of having me only for certain period of time will do for them and definitely for me.
Does any one know how to calculate professional fees in a service like this?

Cheers

I guess you want to charge the highest rate that you can get away with, while still getting the work. It is not a matter of a calculation - you'll just have to see what rate the market will bear.