For several years in a row we stupidly invested in expensive pre-feb screen rooms for buggy summer evenings. None of them survived through the next season. We decided to build our own. The original idea was a very simple screened in structure, but we managed to save a ton of money by purchasing some of the supplies through our local Habitat for Humanity Restore (selling used or donated building supplies).
4X4's for the main posts
2X6's for roof frame
2X4's for body frame
aluminum roof panels
finished fiber cement siding
Once the frame was up, we put in the roof brackets and 2X6 brace pieces. We managed not to get decapitated by the aluminum roof panels. Invest in some good gloves for this if you try it- the panels are sharp. The roof pieces require special screws- they're colored to match the panels and have a rubber gasket to prevent leaks. Talk to someone at the build desk for help. (We got most supplies at Menards, and they were crazy helpful)
Once the roof was secure, we finished the framing and put on a good outdoor stain. Don't go cheap on the stain- you want something with UV protection and good waterproofing. (We used an Australian Oil because our dog is an Aussie Shepherd and we wanted something from her homeland)
After the stain had a good day to dry, the screen went on.
The siding got screwed on next. It's kind of like pressed fiberboard, but came pre-primered. After it's all installed, we painted it with a good exterior paint and used furring strips as trim.
Finally, a bit of outdoor carpet stapled to the deck floor, and moved in a bit of the essentials, and the rest is relaxation!
We didn't keep track of the total expenses, but estimate that we put in about $1000 -$1200. We put up cheap shower curtains on PVC pipes mounted under the roof to keep the rain out during summer thunder storms.