What is the standard rental commission to a realtor on office building space for a long term (10yr) contract?

There are no standard commissions in real estate. Check office lease rates on this site and note the commission or call the agent.

There is no standard. Everything is negotiable.

As said by other respected members there are no standard commission rates. The rates for leases exceeding one year might be broken down into different commission rates. To give an example; the realtor might suggest commission rates as 3%, 2%-2nd year, 1.5% for subsequent years. This means that you will pay commission at a rate of 3% on annual net rent (TMI excluded), 2% on next year's net rent, and 1.5% for the remaining 8 years.
If annual rent is, say 10,000 dollars, then the total commission payable is 3% of 10,0000+ 2% of 10,000 and (1.5% of 10,000 X8). The total commission in this hypothetical case equals $300+200+(150x8)=$1,700. Please let me know if I am wrong here. Thanks

Fixing commissions is a violation Federal law. Any discussion of commission could constitute a violation of the Sherman Act and could wind you up in Federal Prison.

Linda....
Whatever is fair and equitable. You must know the space, the owner's asking price for the space, how difficult it is for the owner to lease the space, how valuable your client is to the owner's building and a general feel for what others may be charging in your area. (This can be determined through experience). These things and your own sense of value for the profession you are in will determine the commission you charge. Give the service, fill space, enjoy your contacts and the commision will be measured more in your annual success.
Good luck in all you do and always remember "Onward and Upward"
Rob Baird rob@capratecommercial.com