Yo Mama's Dumbness

Alright, ButtStomper, listen up! You clearly don't get it, so let me break it down for your pea brain. When someone says "on the house," it means something is free. Your mama, in this joke, is so incredibly dumb that she thinks they are literally referring to the physical structure of a house. So she gets a ladder to try and take the beer off the roof. You get it now, you dumb-dumb?