If I had it to do over again, I would use the DOW boat dock plans, but not the DOW Styrofoam Floats. This material dents and chips very easy and also it isn't environmently friendly. The ducks like to eat the algae off them and injest some of the styrofoam.
There is another company that makes a hard black pvc material that does not break down. I purchased the DOW product w/the diminsions of 18"x2'x8'. They sell for about $65 to $90 dollars per float (I used 25). The black pvc sizes are smaller (around 2'x2') but are more bouyant. Even though they are a little more expensive, they will last much, much longer and look better. The DOW styrofoam starts out w/a bright blue color but over a one to two year timeframe will turn a light green color w/the ugly algae around them.
I can get the name of the manufacturer of the black ones' if you want.......