I need some help regarding a CB Antenna?

the best attic antenna would be a loop of wire strung in the horizontal plane that is 1 wavelength at CB frequency. That would be 34 feet total length if that fits your attic. layed out 'square' that would be 8.5 foot on a side, but shape is not critical and 6 x 11 rectangle will be just as good. where the ends come together is called the feed point. that will have a 120 ohm resistance. it is hard finding a balun of that exact size for connecting to the coax unless you wind your own. you can use a commercial 1:1 balun and then run about 7 feet of RG6 (75 ohm coax, like used to match twin antennas) to transform to regular 50 ohm coax like RG58 or miniRG8 that should get you close to a low swr.