Definitely not on the north side. You won't get sun in the winter, just tremendous heat loss.

If you are talking about one of those "all glass" sunrooms, there is no good place to put it. From an energy standpoint they are terrible--either too hot or too cold.

All you really need is a south facing room with plenty of windows. The critical part of the design is to get the proper roof overhang for your latitude. (actually this applies to any south facing rooms.) With the proper roof overhang you will receive plenty of warm winter sun but the windows will be shaded in the summer when you don't want the solar heat gain. Passive solar with proper roof overhang is one of the cheapest, most cost-effective things you can build into a new house.

There are internet sites that help with the designs. Just google passive solar.