All you need to build a simple VHF or UHF 1/4 wave groundplane antenna is a coax chassis connector and number 12 or larger wire scraps. Solder the vertical element to the center conductor and attach the radials with nuts and bolts to the four corners, then solder each corner.
http://www.amsat.org/amsat/articles/w6shp/ant_tips.html
Metal garage doors may be solid and secure, but they are not transparent to radio waves. If your garage has aluminum siding, you may experience frustration with the operation of your garage-door opener.
http://www.edn.com/archives/1998/021698/04di.htm#Antenna extension
A ground plane antenna is a very simple antenna. It is a quarter wave vertical radiator and four radials that simulate a ground for the radiator. It directly matches to 50 ohm coax and should show a VSWR of 1.5:1 or better at its center frequency.
http://www.northcountryradio.com/Articles/groundplane.htm
The discone antenna is a vertically polarized antenna, and consists of a flat disc of about 0.17 wavelength diameter at the lowest desired frequency, with the disc plane horizontal, mounted atop but insulated from a cone that has a length of 0.25 wavelength on the side.
http://www.northcountryradio.com/Articles/discone.htm
Here is a nice GPS antenna for APRS mode that is easy to build yet offers surprisingly good performance in a compact size. Best of all, it uses commonly available components and materials.
http://www.arrl.org/tis/info/pdf/0210036.pdf