Sky builds are the devil, especially because side placement (horizontal) building takes forever compared to vertical building with jumping! A way to place 3 or 4 blocks in a row horizontally would be fantastic. Maybe a 3x3 block placing tool?
Rotation lock for blocks on floors would help too; floors can be annoying since blocks get rotated based on highlighting not based on player position like in Minecraft; since many blocks have different visuals depending on rotation of placement, this can make building floors tedious.