This is more under the purview of architectural and building nomenclature as far as distinction is concerned. Here you are:
Keep in mind that the regional differences in word usage can often be on account of varying climates. For instance, New Englanders experience many types of inclement weather, and often have porches which are covered, so that they can be enjoyed for most of the year. On the other hand, people in Nevada often have patios as it is most often sunny, and there is no need for a covering. Respectively, a region will usually generalize to the most common structure, and so New Englanders (I am one myself) will often use porch for veranda or even sometimes deck.
Hope this helps!