Greenhouses, Sheds and Sun Rooms - patio room

I have an interior room about 20 x 20, with three exterior walls. I want to make this into a "patio room". I want remove the three walls or portions of them and have a sreened poarch but with windows that can open. It has to be weather proof because of the floor which is wood, and so It can be heated in the winter.I have looked at these patio systems but they are costly. I would like to know if there is a less expensive way. Any suggestions would be appreaciated, thanks.

Reframe the 3 walls so you can install three 6 foot wide windows (or french doors?) into each wall. But install quality windows (or doors) with low-E glass. Without the low-E glass, you will create a room that will roast you out in the summer, and it will cost you a fortune to heat it in the winter. I would also install a door (or doors) that would allow you to shut this room off from the rest of the house.