Begin by attaching a ledger board from a 2 by 10 piece of lumber to the back of the house. Place the board against the house and mark with chalk. Use the level to make sure it is straight. Hammer the board in place with nails.
Add 2 by 10 joists on each side of the the ledger board. Run a bead of wood glue on each place where the wood meets and join the wood with diagonally hammered nails.
Mark the places for the other joists on the ledger board every 16 inches. Hammer in 2 by 10 boards on these marks and place a bit of wood glue where the boards meet to ensure a secure attachment.
Add a front ledger board with a 2 by 10 board and hammer and glue in place. Be sure to hammer in at least two nails to connect the front ledger board with each joist that has been placed every 16 inches.
Cover the top of the floor with plywood boards. To make things easier use a stud finder to hammer the plywood boards in place on the top of the floor.
Build the frame of each wall much like you framed the floor. Take four 2 by 10s and create a square frame for them. Mark every 16 inches on the inner side of the top and bottom. Add joists where you marked these and hammer and glue in place. Repeat this 3 times.
Cut pieces of wood from your 2 by 10's into several 16-inch sections. Add these for support half way up each joist and hammer in place horizontally.
Cut a two 2 by 10s diagonally on each side and hammer them together on the top of the front wall in a triangle shape. Add a 2 by 10 at the center top of the triangle for the frame of the roof. Attach 2 by 10 joists on each side every 16 inches. Be sure to cut the joists angular so that they will be flush with the walls they are attaching to.
Raise the front wall and hammer and glue the top beam of the roof in place to the house. Hammer the base to the floorboards along the studs.
Raise both side walls and hammer the roof joists to the top of each frame. Using a stud finder and plywood boards hammer the roof in place on both sides.
Hammer the roofing shingles in place starting at the bottom and working to the top being sure to leave at least two to four inches of overlap. Use a ladder to get to the roof and have someone spot or steady the ladder for safety.
Measure the window screen and cut it for each frame section of the wall. Staple in place with a heavy duty staple gun. Paint the interior and exterior as you like or stain the wood and use a waterproof wood sealer on the walls.
Measure and lay down your linoleum or carpeting across the floor. Now all that's left is to grab some patio furniture a glass of lemonade and enjoy your simple but relaxing sun porch. You can make this very basic design more complex by adding glass pain windows and electrical wiring for a fan or lights but please consult a professional before doing so.