The route VW use for either roof aerial or hatch aerial is down behind the C pillar trim drivers side to the floor under the carpet and up to the stereo.
as its only a DAB signal going though a screened cable quite capable with rejecting interference you can run it the easiest way possible, across the head lining is quite an easy route as it can be tucked in the door rubbers and behind trim without removing it.
but if you like removing trim etc. to the floor and under the carpet would be best only IMO of course