Do You Have a Formula for Overall Budget

Every year, creating an IS budget for our company is a major hassle… at least for the people who have to justify the numbers.

I have been looking for surveys, studies, reports on the state of any industry that indicate how much is typically spent on IS/IT as a percentage of gross (or net) revenue.

Right now my company spends around 5% per annum based on our gross income. Is this high? low?

Any thoughts, links, input would be greatly appreciated. (We are in the architectural industry for reference purposes)