Specific Sky Installers generally will not enter your attic space. I believe it's to do with insurance, or lack of.
Drilling a roof tile isn't really a good idea, IMHO. Maybe put dish on a gable wall, and drill through to attic space? Of course, this is only possible if your house is detached on the side the dish needs to go on.
If you want a good job done to your spec, it might be worthwhile going to an independant sky installer/retailer instead like a local electrical shop.