What do the manmade structures in Sense and Sensibility tell us about the societies in which the characters live?

I would interpret the question to mean social structures. The manmade social structure that tells us the most about the society in this novel is patriarchy.
Patriarchy is a system in which men are in charge of society, and a person's last name is passed down from one's father. In this system, property is most often handed down from father to son or the closest male heir. Women are grafted into this system through marriage, and women who are unmarried are marginalized.
The novel shows how the Dashwood mother and sisters are edged out of an inheritance by male heirs and forced to leave their home at Norland to live in a much smaller house called Barton Cottage. The injustice of this kind of privileging of men over women is implied through the fate of the daughters, rather than stated outright.
Because marriage is what confers status on a woman, Elinor and Marianne Dashwood are forced to endure the snobbery and belittling of married women like Lady Middleton who are actually lesser people than they are. The final piece-de-resistance of an unworthy woman climbing the social ladder through marriage is the conniving and low-minded Lucy Steele managing to marry the wealthy Robert Ferrars. She has clawed her way into a position where as Lucy Ferrars (some scholars believe Austen meant her name to be read as "Lucifer") she can lord it over other women, not because of personal worth, but because patriarchy rewards married women. Austen most certainly did not condone this system.

The man made structures throughout the text of "Sense and Sensibility" are, for the most part, all houses of varying sizes. Most prominently featured is the estate of Norland Park. This sprawling house sits on an impressive acreage and is beautiful and intricate in its design, while also being expansive and all-inclusive, showing its grandeur.
This structure is a clear depiction of lavish living, wealth and extravagance, and is juxtaposed thoroughly against Barton Cottage, a modest, ascetic dwelling in Devon. This cottage, while being small and unassuming, is filled with much more warmth and vivacity than the expansive Norland Park estate.
These two abodes show two contrasting characteristics of society in the time of the writing - that of the wealthy and extravagant, who spare no luxuries but lead lives of more lonesome existence and also show more greed and lower moral fiber, and that of the low-class individuals who live rich lives connected with their townsfolk and engaged in affairs of good-nature.