I too am a general contractor and have been part of many secret rooms and hidden doors.Some for security and some for fun.
The problem here is , don't plan and build a $10,000 safe to secure $5,000 worth of valuables. Secret safes and secret rooms are fine but try telling your wife you are cutting the size of her walk in closet in half , so you can build a secret room for your coins and see what happens.
I have the money and ability to build whatever I want, but find a mid range safe, anchor bolted to a wall, secure enough for any needs I may have. Along with not advertising what valuables I have in the house.