Cookie sheet... LOL.... what is your match???
I'm afraid that may not be a big enough ground plane. If you want a
better ground plane you need to run some radials (maybe four or more)
that have perhaps a quarter wavelength length. You could use aluminum
grounding wire which is available from Radio Sack. Keep in mind that
signals in the CB frequencies have poor penetrating power through solid
objects... like your roof. You'd do much better to move whatever
installation you choose outside.

Professor
www.telstar-electronics.com