For a utilitarian solution when appearance isn't as important, consider roll roofing, which is made of materials similar to composition shingles but generally not as durable. Be sure to check the warranty, which may be for only one year. If you install roll roofing using the double-coverage method, it will last longer.
Roll roofing is often installed over bare wood sheathing or sheathing that has been painted with a primer. Applying roofing felt first will better protect the sheathing against condensation, as well as against leaking.
If the roof is sloped, you can use the exposed-nail method. For a slightly sloped roof, use the concealed-nail method shown. For a flat or nearly flat roof, use double coverage, although a torch-down modified bitumen or EPDM roof is a better solution.
Working with a helper, expect to spend half a day installing flashings and roll roofing for a 700-square-foot roof with modest complications. Prepare the roof by tearing off the old shingles, or by preparing for a reroof. Since this is the least difficult of roofing materials to install, only basic carpentry skills are needed.