If the house was not initially designed for the extra storey then, in the same way as required with a timber house, foundations and walls have to be checked and may need to be strengthened. If you want to move load bearing walls it is wise to use an engineer who has experience with steel framing. The big advantage of a steel wall is that it can be disassembled and reassembled in position with just a screw gun. However, the amount of work required for this will be similar to that with a timber framed house.