Cost of Building Basement

1.If the hose has a slab or basement(let’s say the footprint is 20ft. × 25 ft.), in either case you will lay insulation on top of the wall and place a pressure-treated (PT) 2×8 sill plate all around the edge. That amounts to: 25ft.×2 + 20 ft. ×2, Which comes to 90 ft. of PT 2×8.

If you have a basement, you will need two 20 ft.-long beams that will run across the basement and support the floor joists. These beams will be 5 1/8 in., or you can use smaller beams with a single post in the middle of the basement floor.
If you have a slab in a warm climate, you can simply tile over the concrete. In a cold climate, you might want to lay a moisture barrier, and then put 2×4s inside the sill plate. You can lay foam insulation between the 2×4s and cover the entire structure with 3/8- in plywood.
Separate the floors, walls, and roof. Each wall will be made up of studs, headers, and top and bottom plates. Count the number of studs and the total linear footage of the headers and plates and multiply by the cost per item to come up with a price. Add in the wall covering (such as Tyvek ) and then calculate the total wall area to find out how much sheathing you will need.
The floor is made of 10-ft.-long 2×8s resting on the walls and the transverse joists. Count the number of floor joists you will need and price them.
The roof should also be priced out by breaking it into its component parts (rafters, joists, sheathing, and roof covering).
You will need to add nails or screws, caulking, and possibly glue.
Count the exterior door(s) and price each one. Then count the interior doors and price them.
Count the windows and price them out.
When all is done, add in at least 10% or so. You will usually not busy all the materials at the same time and prices may fluctuate.