I was looking at the housing vendor and notice they have House Small tier 1-3, and House Medium tier 1-3. I think I read that the tier 2 and 3 isn't something you buy and plop down but used to upgrade the earlier tiers, is that correct? But if you want a Medium House, do you start with Medium Tier 1, or do you need to work up to a Small Tier 3 and then upgrade that to Medium Tier 1?