I need some help regarding a CB Antenna?

Mounting a high gain antenna in the loft defeats the point of having a high gain antenna as the attenuation created by loft mounting negates any gain in the antenna. Loft mounted antennas suffer from anywhere from -10dB (10 times) upwards which, in the worst cases at UHF, can be as much as -40dB (lots, -10^4). You'd be better off chucking a long wire over the roof with the help of a tennis ball and tuning it with a decent antenna tuning unit (ATU). A bit of tuned 22 gauge wire insulated wire with a dark colored insulation is practically invisible from a distance and would be far better than any contraption mounted in the loft space.