Measure the site for the porch with the tape measure and write down the exact measurements. Sketch the design in detail. Write down the amount of concrete needed for the porch foundation or yards of concrete needed for porch footings that will support a wooden foundation.Concrete estimators for various projects can be found online.
Estimate how much lumber is needed to build the porch framework. Count 2x12 inch boards for support framework. Flooring and roofing will require these boards every 18 inches. These larger support boards will need to be installed to support plywood sheathing on the roof or porch decking. Use 2x6 inch boards for floor decking on the porch. Estimate the cost for salt-treated lumber for all components of the porch.
Add up cost of plywood sheathing in 4x8 foot sheets for the roof area. Use exterior-grade plywood. Add up the cost of tar paper, asphalt shingles and stainless steel flathead roofing nails. Ask a hardware store sales person how many pounds of nails would be needed for the size of porch you are building. Inquire as to whether you can return any unused materials.
Figure in premade posts or scrollwork railings. Ask a store sales person to help you estimate these costs. Buy these materials in hardwoods vs. soft woods for a longer life span. Hardwoods, such as oak or cedar, are excellent for this purpose.
Estimate the cost of paint or stain for the porch. Add the cost of freestanding steps or the cost of constructing steps. Figure in plywood and wood trim materials that will box in the end of porch rafters for the soffit areas and underside of the roof area. Use exterior-grade plywood. Check out the price of hiring an electrician to run wiring for porch lights and the cost of wiring. Add in the cost of one or more light fixtures, if necessary.