I'd be happy with some dimensions. If it's square/rectangular, what are the lengths? if it's circular/round, what's the radius or diameter.
Trust me; not one of the flat earthers here will be able to give you any sort of definitive dimensions backed up with
empirical evidence. The proposed dimensions of their flat earth are entirely dependent on which flat earther is telling the story at the time, and has no basis whatsoever in reality.
They use a sort of nebulous agglomeration of hearsay, conjecture, fancies, guesstimates, factoids, and imagination in order to come up with any sorts of figures at all. It's actually quite amusing to watch different flat earthers propound their own personal theories about the purported shape and size of the planet, whilst none at all can agree on a common model.
So I wouldn't hold your breath waiting for any sort of "accurate" answers to your question.