Could you please cite the Scripture that says the earth is flat? As for the dome over the earth, that could be understood as the atmosphere, taken metaphorically, or else some (typically Protestant) scientists posit the existence of a water canopy above the atmosphere that, when it collapsed, led to the Great Flood. With regard to the "four corners", does this mean your vision of Flat Earth is rectangular (vs. round)?
So far, as I understand it, the math of planetary movement, the movement of the sun and moon, and the change of seasons makes more sense as a sphere vs. flat. But I'm still studying.
It is unlikely that the Genesis passage could be understood metaphorically. It reads:
6 And God said: Let there be a firmament made amidst the waters: and let it divide the waters from the waters.
7 And God made a firmament, and divided the waters that were under the firmament, from those that were above the firmament, and it was so.
8 And God called the firmament, Heaven; and the evening and morning were the second day.
Also:
14 And God said: Let there be lights made in the firmament of heaven, to divide the day and the night, and let them be for signs, and for seasons, and for days and years:
15 To shine in the firmament of heaven, and to give light upon the earth. And it was so done.
---------------------------------------------------------------------------------------------------------------
God separated water under the firmament from water above the firmament, and called it heaven. The saints actually expound on this at great length. But for one short citation, St. Cyril of Jerusalem followed Basil’s teaching and was a flat earther, using quotes from the Bible portraying earth with firmament floating on water using Gen. i. 6. He wrote in his Catechetical Lectures: Lecture IX: “Him who reared the sky as a
dome, who out of the fluid nature of the waters formed the stable substance of the heaven. For God said, Let there be a firmament in the midst of the water. God spake once for all, and it stands fast, and falls not.
Severian Bishop of Gabala taught the same thing Cosmas did regarding the earth. Earth is seen by them as a "tabernacle", a house, or a Church. (So in answer to your question, it seems to me, that it probably is somewhat rectangle overall, with a circle of land circuмscribed within it as scripture says; it has a dome, pillars, a foundation, and appears that it may look something like a Cathedral.)
Bishop Severian says
He made the upper heavens about which David sang: "The heaven of the heavens is the Lord's."6 This heaven forms in a certain way the upper stage of the firmament. As in any two-story house, there is an intermediate stage; well in this building which is the world, the Creator has prepared the sky as an intermediate level, and he has put it over the waters; from where this passage of David: "It is you who covered with water its upper part.“Cosmas is a little clearer:
Moses, likewise, in describing the table in the Tabernacle, which is an image of the earth, ordered its length to be of two cubits, and its breadth of one cubit. So then in the same way as Isaiah spoke, so do we also speak of the figure of the first heaven made on the first day, made along with the earth, and comprising along with the earth the universe, and say that its figure is vaultlike… and God [130] having then stretched it out extended it throughout the whole space in the direction of its breadth, like an intermediate roof, and bound together the firmament with the highest heaven, separating and disparting the remainder of the waters, leaving some above the firmament, and others on the earth below the firmament, as the divine Moses explains to us, and so makes the one area or house two houses----an upper and a lower story.One more thing: God put sun, moon and stars "in" the firmament. How can the sun, a million miles in diameter, 93,000,000 miles away, sit "in" the firmament? Under the dome? Above which, is water?