This cable is the best quality, see article on copper/copper satellite grade cable.
And don’t forget cable clips, you’ll kick yourself if you do……
The cable is just as important as the aerial (and any amp or splitter, if fitted) in providing a decent signal on your set. The cable should be changed as a matter of course if any work is undertaken on the aerial, unless you are sure it is sound and of good quality.
A typical cable run (from the roof) is about 15m. Bear in mind that it is preferable to order a bit too much, than a piece that’s a bit too short….. Any extra cable can be made into fly leads, which, I guarantee, will be better quality than those you already have.