How much would a room extension like this cost?

I am wondering how much a certain type of home extension/addition would cost. The basis is this... If someone were to extend a 20-25 foot section of wall in thier home outward about 10 feet, using only the concrete foundatuon of the extension as the floor, how much would that cost. Im merely looking for a very general round-about answer. The idea here is only to use contractors where absolutely necessary, and do most of the other work with friends and family. For example...say someone has a one story rancher, and thier living room is 25'x20'. If that person wanted to extend the 25' wall outward 10' on thier property, making the new dimensions 25'x30', without adding any interior drywall, flooring, electrical, or plumbing...just a very bare room extension...how much would that cost. A foundation is obviously a must, but all that would be needed for this build is walls, a roof, and exposed insulation.