it could be a circle within a square-type set up....maybe, even, with a semi-raised hemi-spherical section....
that would be compatible with what the Bible says, re: "the four corners of the Earth";
the fact is and as You-tuber "Mark Sargent" has pointed out.....no-one really knows......or, rather, no-one alive today really knows (except, maybe, for TPTB) because no-one has passed that 'outer boundary'......Sargent claims that Admiral Byrd passed it but he either chose not to tell what he saw or its been buried..
(http://i136.photobucket.com/albums/q197/__jimbo__/1280px-Orlando-Ferguson-flat-earth-map_edit.jpg)
*note*
the above Orlando/Ferguson model leaves out the glass sky dome ....as per the Book of Job
(actually, now that i look @ it, this is a very good model {apart from the omission of the gsd} because it, also, accomodates "the concave Earth theory", to an extent.....for which, apparently, there does exist some support)
*note*/edit
actually....i'm a smidge dubious about the "raised hemispherical portion" for two reasons:
i/it conflicts with the massive evidence for 'flat Earth horizons' and, even, the flat Earth vistas seen from 'space' by amateur rocketry;
ii/it was, apparently, introduced to 'account' for "the Columbus phenomenon"; i.e: ship masts "disappearing" over the horizon.....a phenomenon easily explained by the peculiar "pyramidal vision" of humans;
that said: the model could, still, be mostly accurate....with say......a circular Earth 'recessed' into a huge, flat, slab....and, still, with concave sides....