Figure out how much to enlarge the floor base. Construct a couple of extra feet of concrete flooring on each side, for example. Plan to build the base out of the same materials used in the original porch. Cover the entire dimensions of new floor space with tile squares to tie it all together.
Make plans to extend the roof on each side to cover the new floor base area. Plan to remove old asphalt shingles to build additional roof framing. Cover the new roof with sheathing and install new asphalt shingles to cover the whole roof.
Build the porch foundation extensions first. Choose a time when the weather is good to construct the flooring. Order concrete for a concrete pour instead of trying to mix it all yourself. Build the porch floor area bigger than the new roof will be, if you desire. Keep in mind that the roof design will affect the overall porch design more than any other aspect of the project.
Construct additional roof sections by adding approximately 3 feet on each side. Secure the framework to the house framing with bolts, because screws are never strong enough to hold this kind of framing. Install plywood sheathing ½-inch thick and cover it with tar paper. Add asphalt shingles that match the house shingles. Install copper metal roofing as another option. Replace guttering with larger sections for the added porch materials.
Improve the look of the porch with columns and railings. Buy a couple of well-made wooden posts at a home improvement store. Select posts that are large enough to give the visual feeling of added strength to the structure. Buy posts that are 12-inches square, as one option. Install new railings that tie the porch base to the house design. Choose railings with square balusters, for instance.