[juanbenae]

3-4-5,, you may be asking what the hell is 3-4-5, use multiples of 3-4-5 to check to see that your corners are square. measure say 9 feet one way, 12 feet the other on a corner, the hypotinuse (sp?) will be 15 feet. a corner to corner diagnal should be the same didtance.

if you have expansive soil in the area you will want to cushion the slab with some compacted base rock. this will also help minimize cracking. an expansion joint along the slab where it meets the foundation is advised. 40" footing for frost? i thought building in california was bad with the earthquake requirements.

last hint,, find some guys that can finish concrete on pour day and pay the going rate. unless you want a nonskid rake finish you need to have at least one guy skilled at concrete finishing. a 20x20 slab can get away real quick in warm or windy weather.. keep it moist during cure in hot weather.