Basement addition suggestions would be to make sure the basement is basically dry and to waterproof the walls or by complimenting the existing draining system before any framing. Basement additions also may be complemented with a finished floor. Additions with intentions of finishing the floor also have various options. The least expensive is a concrete paint, sealer, or epoxy. Carpet is another means, but must be the type that is made for concrete floors. Laminante or the new rubberized 100% waterproof floors are the most prefered and very popular types.
The highest quality floors to lay pressure treated sleepers to the existing concrete floors with power hails and adhesive. Then attaching plywood to these sleepers, creating a subfloor that can have most finished floors or any types of carpet. Basement additions with a full finished floor is the more expensive type, but offers a floor that can accept any type of finishing that can be changed at any time. Another basement addition type floor is using tile, but this type requires having a very good quality smooth concrete floor to start with. You can also use floor a leveler to smooth an existing floor that is not smooth.