Fort building is a great start package for building style games. it is still in development but you can get the updates when the come out for free.
In this demo you can :
-build a stair, a floor and a wall
-set the keys you want to use for building and mouse sensitivity
-3 Different materials to build.
-More assets and props likeTrees and houses.
Asset version: 1.3
More Info: _https://assetstore.unity.com/pac … ort-building-130058