Scarecrow in fields/farms are to ward of the crows, but here the application is to ward of the evil eye (aka Drishti). The new building and its owners need all the good wishes for their new venture and hence this scarecrow as a Drishti.
See more of those varieties here, here & here.
Any doubts? 🙂
I think this Scarecrow is possibly Lehman(‘s) Brother! Hanging himself!
Ram: Or the Rajus?
It is a double purpose figure used both in farms and houses under construction. NObody will cast a dhrishti on a semi finished building. If at all , they will do so only on a new building. But the belief is there.
Ram: Hmmm …