I'm sure it would increase the cost of the project by many times and require more complex permits, but just think how cool it would be to access your office shed through an underground tunnel.

But you've got to shovel and clear snow regardless? Shoveling a small path and being careful how you take off your shoes sure beats scraping ice off of a car and dealing with the plows' windrow.

The biggest problems I see is wanting to frame out the walls with 2x6's for thicker insulation, ceiling trusses at 16 oc for snow load and thicker for insulation as well (or lose the headroom and build a traditional ceiling/attic), and of course more heating load from the heat pump.