We are in the process of adding on a porch. In our case it was a way to get rid of a sometime water problem we had in the basement and the ugly" Wizard of OZ storm cellar doors" near the primary entrance to the house and to fix what was there and falling apart. Apparently we are not the first to change out this porch area.
When the construction first began we found at least two if not three other parts of porches that had been in that space. This is the first time however that it's been made as large as it is. We went from the end of the house to the inside corner.
The space is going to have a short wall with windows that open and close with screens. I found six old window/screen sets at a reuse place which saved us a ton of money. We also found a door for the space for free from a friend who had changed some things around in his home cand whose wife wanted the door gone last year! Both the windows and the door fit the age and style of the house.
The storm cellar doors have been removed and a hidden flush with the floor door is being constructed.
We tried hard to make our new porch look as much like it belonged there as we could.
We ever get it done I will post pics.

We added a sun room onto our old house. It sits on top of a cement patio and has french doors which open into the kitchen. The north and west walls are windows and the south and east walls are interior walls. It is approximately 15' by 20'. My husband wanted to put in a wood stove, but we were advised against this for two reasons. One, it would get too hot and the second was that it would take up too much room. So we put in an electric baseboard heater and we love it. We can shut the french doors on really cold days, but we use this room almost year round We also installed two ceiling fans.

We installed a functional, commercial lean-to greenhouse with plexiglass panels against one ell of our house. Put in a gas fireplace and it is heated in winter and used year round. It is 12 x24 and multifunctional now. We keep it heated in winter, at one time it was used as an office for my business, and forced into use as a place to overwinter nursery stock for propagating. Since my business has been phasing down and is now phased out we simply use it now as a great buffer zone against the elements. My back door and two other household doors remain open to it year round. I have a fountain in there and hang ferns in winter. It has brick floors and is a great transition room from our outdoor activities to inside activities.......home for coat racks, boots and animals who shoot out our back door without leashes, lol. Gets a good amount of solar gain and helps our heat bills too. We have a ventilator fan at its apex to pull out heat, have a shade cloth we can use in summer, and a storm door for the outside entrance, so we can screen in summer. I can't imagine not having it now and it's a lot handier than the creaky old back porch we pulled off. It's like having both functional outdoor and indoor space added.