I stumbled across a photo of a model of what would be Shea Stadium, except this version is completely round! The photo comes from a 1961 story in The New York Times reporting on the stadium’s approval.
Aside from the completed circle, there are two other things of note:
It is interesting that there is a football field rather than a baseball field in the model of Shea Stadium. The Mets did not exist yet in 1961, so maybe they weren’t sure that the city would really get a baseball team, so they went with the football motif.
Also, the design was so far along that those famous blue and orange panels are on the model.
Here are some better images of the model, courtesy of StadiumPage.com: