I built a couple, then ended up buying this one: http://www.antennasdirect.com/store/DB2_antenna.html
, which was only $30 at the time. Works great in my attic.
But most any UHF TV antenna design will do. Nothing magic about HD or "digital" antennas. They are most all UHF. My buddy in San Francisco built several "Digital TV" antennas out of oven grills, a couple toaster grids and some coat hanger wire based on the design of the one I bought. That might give you some ideas.