OK, I'll go first.
Is the building built yet? If not, then you need footings around the perimiter to support the walls. The depth of these will be area specific, so I can't help you there. Here, we go a foot down and a foot wide. Other places it might have to be several feet deep.
If your building a pole barn and don't need footings, than 4 inches is fine. If your gonna parks some heavy equipment on it, that you would want to go with 6 inches.
I hate wire. Technically it's stronger than rebar, but it has to be centered in the middle of the pour to be effective. Every study I've ever read on it suggests this almost never happens throughout the entire pour. Usually it will end up at the bottom of the pour and provide zero benifit.
What happens is the crew pouring the cement will pick up the wire and pull it up into the mix while walking around on the wire. It's real hard to keep it in the middle of the mud while walking around on it and there's no way to know if it's there once they move on. The only time you realize the wire failed is when you have a crack.
Rebar sits on chairs of some kind. I use plastic because they are cheap and easy to use. Some people use rocks or concrete chairs depending on their area and preference. They hold the rebar in the middle of your mix and it's pretty hard to screw it up this way.
3/8 rebar on 2 ft centers is pretty common for pads. Footings usually need 1/2 inch and should run the entire footing. Depending on the depth of the footing, I run two lines 6 inches above each other with the 3/8 rebar bent down into the footings.
A friend told me that in Florida they are now requireing 5/8 rebar on 12 inch centers!! Hurricanes.
I've never used a vapor barrier. It seems to be fairly common in the Northern States, but rare down here.
More important is your base. Sand is best. If you have to fill, be sure to do it in lifts and get it compacted. If it's not compacted well, it will settle over the years and your foundation will crack and settle. Lots of homes were built like this and the problems they have is something terrible.
No matter what you do, be sure to have a crew who knows what they are doing do it for you. This is not something you want to try to learn how to do yourself. It's backbreaking work that you have to get right the first time!!! Any mistakes and your stuck with it for ever.
Eddie
