When did tipis begin to be used? When did they stop being used?
Where geographically in NA were they used? Were there any environments they were particularly well suited for?
How often did they deconstruct/reconstruct the tipi? How often did they completely replace the materials of the tipi/build an entirely new one? How long did it usually take to harvest the materials and then build one? For what purposes did they use the tipi? Were there specialist forms of tipi for unique purposes?
Who actually used the tipi at time of first contact and were these groups the originators or was it relatively wide spread?
Other questions I had include:
Did these people have other buildings/structures they also used for separate purposes?
Were there other people sympatric with them who did not use tipis? What did they use?
How and when did the tipi become the stereotypical Native "building"?
Are there other Native American buildings/structures that were much more widespread in usage or characteristic of a much greater portion of the population and what the living conditions of the New World were?
Tipi, tepee or teepee?
EDIT: Spelling and formatting.
Housing is as varied as resources and needs. looking at tepees, meaning specifically the large, tall tents, with around ten to twenty poles, made out of a dozen or so buffalo hides, they were used by people who made their living primarily hunting buffalo. I can't say when they began being used, and can tell you that they are still used by some people, though often not as permanent residences.
People who followed the buffalo included many of the Siouan peoples, many Cree people, as well as blackfoot, and others further south.
Among those who did not use tepees, a wide range of other buildings were common. People who lived in the far north (still trees) made cabins, used tents, or very small versions of tepees. Others made houses out of rocks and sod, even in the high arctic such houses were used year round. In more resource rich areas of BC permanent buildings were very common (meaning the buildings were permanent, not that people always lived in them), including kikwuli houses (pit houses) and cedar long houses.
As to the question of sympatric populations, while the answer is yes (for example the Metis, who survived in part by trading and fishing) might have cabins in the same areas where the Cree (who were buffalo hunting and doing more gathering) might be primarily in tents, for the most part people in the same areas lived the same lifestyles and used the same dwellings, and even in the case mentioned (Cree and Metis) cultures overlapped massively, and people passed back and forth from one style to the other from time to time.
A relevant question about the tepee would be: how much did the introduction of the horse lead to the spread of tepees? The growth of buffalo cultures after the horse would, I expect, have lead to an increase in tepee use, but I don't know.