We completed a solar greenhouse built onto the south wall of our octagonal house just about a year ago. This is in West Virginia, zone 6. It cost a little less than a thousand dollars in materials, and is 8' by 12'. So far it has served all the purposes I hoped for it quite well, except that it's a bit small for a good hangout spot--when I've left a chair in there, it's gotten in my way. I generally found it TOO bright for reading anyway. Because we have large hickories overhanging the house on the southwest, we had to build a solid metal roof over it (the falling nuts would have cracked glass or plastic) But there is another roof under that, and the south end has glass; in winter the low angled sun shines through but in summer it doesn't. The greenhouse, which is adequately vented, did not make the house hotter in summer thanks to that shade. On sunny days, even in winter, I have to open the vents (including a screen door to the house, where it often adds desirable warm air). I figured I could bring my plants through a cold night by leaving a metal bucket of coals from our woodstove in there--but last winter was so warm I never needed to try it. We have three barrels of water for thermal mass and one with holes for compost, for CO2 and a little extra warmth, across the north side The biggest negative of this design is that the greenhouse cuts down considerably, all year, on light coming into the house from the south, previously the best-lit section. One part of this is the cheap but permanently stained sheets of glass we used--a bigger part is the solid roof. If you have nothing dropping objects onto your roof and use glass or plastic, you will have less of a problem with this but perhaps a problem with undesirable heat in summer. The perfect situation, if you had a big slope to the south, would be a greenhouse mostly below the south side of the house, so your south windows could look out over the top of the greenhouse, which could vent warm air up into the house.