Jen - what you need to do is to 'scribe' a wood frame board against the stone on both sides of your opening. Here is a link that shows you how to do it - www.thisoldhouse.com/toh/skill-builder/0,,212554,00.html?xid=yahoo-answers&partner=yes. This will bring your wood frame board tight against the stone so that only a small bead of caulk will be required. It also gives a more 'finished' look without big gaps between the wood and stone that have to be filled. Be sure and use treated wood! If you're not up for the challenge, any good trim carpenter should be able to do this for you. Once you have the two boards scribed on the sides, add one under the beam at the top and along the bottom that match the profile, and probably a few more evenly spaced vertical members so your 'screens' and 'windows' are a manageable size. Then put a 'stop' all the way around the frame so the 'screens' and 'windows' have something to butt up against when they are installed. Once you have all that in place, all you have left is to make the 'screens' and 'windows' and figure out how you want to fasten them in place. Oh yeah, one last thing - enjoy your new screened porch!

Your picture cuts off part of the deck you seek to cover with the screened porch. Matching the existing roof pitch or altering it to a slightly lower one, as Dy suggests, needs to take the additional area into account. It is a bit of math and some minor geometry...but if the entire deck is be enclosed it is difficult to give a real answer without dimensions. I recommend a local architect or design/build firm consultation as well. A dimensioned plan and elevation may get you answers here...but without that, a tape measure and a creative mind at the site are the best combination to get.

Dyecture & Prestige One - The porch is going to be a screened porch. I'm asking opinions on whether the front gable should be screen or siding. I see it done both ways... Any opinion on the actual gable part?

That view is dreamy! I would put an area rug in the section that seems to have the sofa and coffee table and leave the two side chairs on their own. A indoor/outdoor carpet are best for this space as the fabric tends to be better when weather is added into the mix. The indoor/outdoor carpets tend to be light and easy to move, I don't think it would impede the moving of the furniture but that depends on what you're actually moving around. :)