If you can put up photos as your
project progresses it can motivate a lot of people to try this, or something like it, on their own.
Frame
Lumber is probably the easiest material to work with. Some larger beams for the corners, with studs for vertical supports. The price is low, tools are available, and the glass can be attached easily.
Attach
If left in the existing frame, screws will hold the glass to the
wood structure. There is weather stripping on the market that will offer a seal.
If removes from the existing frame, a wooden frame can be built to hold the glass - much like the panel of a cabinet door. After that, connecting this frame to the wooden structure is a matter of screws and weatherstripping.
Vent
Unscrew a couple of the glass panels.
You can install screen in the holes to keep the skeeters out.
Heat
There are solutions all over these forums. Rather than reinvent the wheel I'll direct you to the Search feature at the top of this page.