So you would need to make a set of minimum 3 levels, that contain different minigames, and program the AI so that you have opponents to play with you.
The building would choose a random level upon each entrance. Not to mention that each level has a damn theme! That's alot of artwork.
I think it's mostly the AI and multiplayer that would take the longest to perfect. Probably 3-6 MONTHS

And you can't even begin to work on the AI or multiplayer until all levels and minigames are done!
But damn this would be one hell of a game =)