What I found is that the biquad descriptions were not really precise. Here are some additional tips:
When you build the biquad out of the wire, you will have to trim the ends. Make sure all your sides are exactly 30.5mm long (middle of copper to middle of copper). You have to trim the ends because the copper pipe has a certain diameter that you have to take into account. So if the pipe is 12mm thick, you have to trim 6mm off of each end of the copper. Got it? That threw me off a bit when I built the antenna.
About the copper pipe: Make sure the pipe is just slightly thicker than the coax you buy, this helps to fit the coax inside of the pipe. That way it's easiest to attach the two to each other.
To measure the effect of the antennas, I downloaded wavemon for linux.
Some other resources for antennas: