Most of my angel lore is taken straight from the Supernatural lore, but there are some things I have fleshed out and maybe a couple things I have changed as well.
Archangels: Archangels are second only to God, but currently the only two known to be alive are currently locked in Lucifer's Cage. They have six wings and their primary wingspan is no more than forty feet across. Their secondary pair of wings has half the wingspan of their primary pair and their tertiary pair is half of that. The only way they can be created is by God or, even rarer, by two archangels mating. God can create them from nothing or by promoting a lower class angel.
Seraphim: Seraphs are one level beneath Archangels and are therefore more numerous, but far less plentiful than regular angels. They number no more than fifty currently. They can be born in a mating between two Seraphs or between an Archangel and a Seraph, but they cannot be promoted from a lower class angel unless God does so. They have four wings and their primary wingspan is no more than thirty feet across, with their secondary wings half that size.
Angels: Angels are beneath both Archangels and Seraphs and are quite plentiful. They number in the very low hundreds, at least. They can be born in any angel mating that doesn't already create a specific type of angel. They are divided into different orders, or jobs, and take orders from the Seraphs and/or Archangels. Rit Zien, for example, belong to one of the orders. They have one pair of wings and their wingspan is no more than twenty feet across.
Cherubs: Cherubs, or Cupids, are the lowest class of angels with their own set of powers and responsibilities, primarily maintaining vessel bloodlines. They also will occasionally have fun creating unusual and unlikely pairings when bored, and it doesn't defy previous orders. Cherubim can be created by a mating between a Cherub and a Cherub or a Cherub and any other class of angel. They have one pair of wings and their wingspan is no more than fifteen feet across.