What are various design factors that influence energy saving in building construction?

I presume you mean that you want the completed building to save energy as opposed to the construction process. First and foremost is holding on to heat (or cold) that you're paying to create (you "pay" for firewood with your time, energy and the various costs associated with your chainsaw and splitting gear). Insulation and sealing inside against outside are the keys to this endeavor. Some of the most highly effective ways of pursuing these goals are "Earth Bermed/ Sod covered/ or Underground construction and the use of vestibules to prevent the wholesale loss of conditioned air when someone enters or leaves. Kind of like an "Air Lock" on a space shuttle (or an as-yet fictional Star Ship). For many folks, siting a house into a south facing slope is not practical. Other factors become more important (they're always important). There are limits to how much you should seal a house (especially in moist environments). Highly efficient appliances, though expensive, have usually paid for the cost difference somewhere from 3 to 10 times over the life of the appliance. In these days of greater energy costs, that number should be greater. Natural lighting can be a huge efficiency factor, as can be having properly calculated Windows and overhangs on the East, South and West sides of your house. There are many good books on "Solarizing" your house plans. one I highly recommend (if you can find it is called "other Homes and Garbage" (a play on "Better Homes and Gardens" magazine title).