[BUG] STAIRS ARE STILL LOCKED AFTER LEVEL 20

Stairs?

Are you talking about the ladder?

Those items require that you first upgrade your commercial buildings to the required level.  So, for example, tap on the Hardware Store in your city (where the ladder is). You'll see at the top it says "Hardware Store" with three grayed out stars (if you have no upgrade stars for that building yet). Tap on the little green arrow to the right of the name and it will bring up the upgrade menu.  Each upgrade you do gives you one gold star, up to a maximum of three.

In order to get the ladder (or other new items), you need to make sure that the commercial building has been upgraded to have at least as many stars as is displayed in the requirements for the new item. So if the ladder shows one gold star as a requirement when you tap on it, then you need to upgrade your building supplies store at least one time.

Does that make sense?

My Ladder showed up today and I upgraded my store as soon as it became available(Probably last week or the week before).  Make sure you install the latest update.  Much Luck! 

You're right ! I thought the tems get unlockéd only with levels but the upgrade of the store did Work for thé stairs juste fine !