Grounding of metal buildings
Whatever satisfies your inspector is probably all that you are legally required to do.
Inspector requires grounding of metal building, I plan to use a rebar in slab to tie to metal frame in another place?
E&S recommend 10-ft ground rods, as this allows you to have 8-ft of the rod below the 1.5-ft mark, and still have 6-inches of the ground rod above grade for bonding purposes. The National Electrical Code (NEC) now requires two (2) of these rods (unless you can measure the rod and prove it is below 25-ohms resistance-to-ground) be installed at least 6-ft apart. You may want to install two (2) rods, one each at opposite corners of the building. Bond the steel frame directly to the ground rods using a solid #6 copper wire (or larger). And yes, ideally the rebar in the concrete should be bonded to the metal frame of the building. We recommend at the 4 corners. Please see the NEC 2011 Handbook for illustrations detailing the bonding requirements of rebar and the steel frames of buildings, as well as how to properly install a ground rod.
The Engineering Experts at E&S Grounding Solutions