This is a little bit off topic but what type of door or electronic lock would you recommend if someone was building a walk-in safe?
This is a tough question, as it depends on the situation.
If it's existing construction, and you're looking for a "vault" door, then the AMSEC is hard to beat. It's light enough to be man handled into place, and dimensionally similar to most interior doors.
If it's new construction, I think the Fort Knox doors are nice. For better security, Graffunder builds some really nice doors. All of these doors will weigh over 1,000 pounds, and are most easily installed during the construction process.
With that said, I think used doors are the best value. You can typically get a 5,000 pound, stainless steel, bank rated door for a thousand or so dollars more than the Fort Knox units. This gives you real security and a heck of a conversation piece. These types of doors can only go into new construction.
If you're wanting to stay away from the vault door look, you can order FEMA hurricane rated doors with multi point locking mechanisms from commercial door dealers. These look like regular commercial steel doors, and are quite secure.