The "twig" is dual band for ham radio... Based on a W7lpn design but insead of using wastepipe and aluminium tube I just made the three mid sections out of thick (RG0213 coax) (all half wave for 2m * .66 (v factor of the coax)), the top section is enammelled copper wire (quarter wave *.95 (v factor of wire in air)) and the bottom section is 15mm copper tube (again quarter wave *.95). Then a few ferrite rings placed about half wave down from the feed point. Tuning is done by moving up/down the ferrites but found it to be a bit low on freq so chopped a couple of inches off the two 1/4 wave sections which then brought the SWR down to less than 1.5:1 on both bands.. 70cm is a bit narrow but only wanted it to cover the repeaters and simplex channels, on 2m it covers the whole band and even covers 446.
Co-ax was from Knights on ebay for £20 delivered for 15m (though only 3m max is for the antenna construction the rest is feed and also for my HF feed) and the 7m fishing pole (only half used and of course it's not carbon but purely GRP) was £13 delivered on ebay and the copper tube we had from removing an old radiator.
Construction ideas were taken from these two sites
Design of antenna
How to cut/connect the coax together
So all together I've got a roughly a 6db(2m)/9db(70cm) antenna for about £15 which if bought from an antenna supplier would cost me £70+
Not sure it would be practical for CB usage as this is basically a one 1/4 over three 1/2 and then another 1/4 waves which in CB usage would be 22meters long
You're better off using a single band cobweb antenna (normaly a half size g5rv (can be bought from a lot of cb/radio shops/ebay for about £20+) and feed that in a square design round the loft space (about half way up) so that the free ends nearly meet. You way need to add a foot or two or both ends to bring it upto 11m from the 10m it'll be tuned to or just use a cheap ATU/Matcher.