Cessna 400 pilot reported while completing their check list with the engine idle set at 900-1000 RPMs and their feet on the brakes; they did not feel the aircraft move until it contacted the hangar.

Narrative

Statement regarding incident at ZZZ field on Day 0 in Aircraft XThis is a hard report to write; professionally and personally. After 38 years of flight instructing I have made a mistake that I have been cautioning clients about since 1989.I was alone in the Columbia 400. I have just under 10 hours in the aircraft over the preceding four months. I am still not as at home in it as I am in all the aircraft I have many more hours in. Therefore after engine start I was taking my time doing every item on the list slowly. I recall that I had only 2-3 items left before calling for clearance and taxi. I was heads down looking at the checklist in my lap. I had my feet on the brakes (no parking brake on - BIG regret) and had set the idle to 900-1000rpm as per the checklist. I assume that as the engine warmed up it gained some rpm as usual. Clearly I was not hard enough on the brakes. I did not feel the aircraft rolling forward. I heard a bang; slammed the brakes as I killed the mixture and saw that it had drilled a hole in the hangar in front of me; damaging the spinner and the prop. It remains to be seen if the damage extends to the crankshaft; engine; firewall; etc. I am grateful that no person or other aircraft was damaged. I am taking all financial responsibility as although I was added as a named pilot to the owner's insurance I just learned that he only has liability insurance. A very expensive lesson!I am already sharing this incident with all of the organizations in our community to raise awareness about pilot distraction.