It's actually very easy, it doesn't involve any drilling, just glue.
When you buy the spoiler from the dealer it comes with the glue and solvent to clean the paint before using the glue. Make sure you have a huge supply of PVC tape and a competent friend, near to hand, with a pair of scissors ready to apply it!
Cleaning the paint is easy! Then squeeze the glue from the tube (it's like black tooth paste and sits in a groove on the underside of the spoiler). It's important to leave a 3" gap in the glue just above where the top brake light sits. You should use ALL of the glue in the tube.
Take a
deep breath and then stick it on the car. It will take about 24 hours to harden, so use the tape (lots of tape, along the whole length of the roof ideally!) to hold it firmly in place for 24 hours. The instructions will say that you should leave it for about 3 days before using a rollover car wash, I would recommend not using a roll over car wash for at least 20 years, preferably
much longer
It's really quite a fun job, but it needs
lots of confidence and (preferably) some shelter to leave the car in for 24 hours. If you are short of either, book it into the dealers where they will charge you about £70 to do the job.
I hope that helps.
Tigger.