Yes it is possible to set up an antenna on your roof AND receive high-definition broadcasts! There are certain types of antenna’s that you can buy, and they range from about $80 – $800. Right now most major networks are being broadcast in digital (DTV), or will have to by the year 2009. If your tv is not digital ready, you will need a box to convert the digital signal to analog.
But let’s get back to the antenna. The CEA has developed a fantastic website that will show you (once you put in your zip code), the kind of antenna you will need an which way it needs to face to receive the signal. It even takes into consideration the buildings around you that may interfere with the signal. Check out http://www.antennaweb.org/aw/welcome.aspx
Of course you need to realize that only free broadcasts will be available. If you want HD programming from HBO or ESPN you will have to subscribe to a cable or satellite provider.