build (something) from the ground up

To construct, create, or develop something that has no existing foundation to build upon; to build something from scratch. This house is a real dump. I think our best bet is to completely level it and build it again from the ground up. I built this company from the ground up—I'm not going to sell it, ever. A: "The engineering department is such a mess right now." B: "I know, the next department head is going to have to rebuild the entire program from the ground up."