Cushcraft made for awhile, and may still build a WARC band vertical that 
tunes 12, 17, and 30 meters. It is called the AWV3. For the speech users out 
there that's A W V 3.

It's not very heavy, but is about 20 feet tall when fully assembled.
It is a 1/4 wave trap vertical, and must have ground radials added, even if 
ground mounted.

It would work well either ground mounted, or roof mounted.

As someone said in another post about the Ham Sticks, you could also mount 
it on a fence post, and use the fence as part of the ground system. If the 
fence is made of wood or plastic, you can run radials along it, supporting 
them with staples or cable ties.

Almost any size of wire will work, as long as you can get a good electrical 
connection to the ground terminal of the antenna.

If you are only interested in single band coverage, try to locate a QST 
article called the C pole.

Basically, this is a half wave dipole made of tubing, that is bent into a 
shape resembling the letter C. Since it's a half wave, it does not require 
radials. As I recall, the QST article gives dementions for 17 and 20 meters. 
Perhaps someone in your area will help you construct one.

I think I saw recently where Force 12 is about to market commercial versions 
of this antenna for several individual bands, including 17.