Make yourself an ark of gopher-wood 
In Hebrew, “gopher wood” is “עצי גפר” — “atzei-go’fehr.”
The traditional English translation reproduces the sound of the Hebrew “גפר” without actually translating it.
In ancient Hebrew, it would actually have been pronounced with the “soft g:” i.e. “jo’fehr.”
What is “gopher-wood?”
If “atzei-shittim,” the Hebrew for acacia wood, meant “wood of (the area of) Shittim,” perhaps “atzei-go’fehr/jo’fehr” might mean “wood of (the area of) Jo’fehr.” There is, in fact, a town with a similar name: “Ja’far is a village in eastern Yemen…” 
“Although ‘gopher-wood’ is a mystery, several authors have suggested that it’s cypress.” 
“A resinous wood, which would not admit the water; probably the cypress.” 
(“Cypress” comes from the Greek κυπάρισσος/kyparissos, the first phoneme of which is “k,” making it resemble the Hebrew triliteral root k-f-r, as mentioned below, more closely than g-f-r. This might be merely incidental, or it might be one more argument for the “cypress” identification.)
“[Gopher-wood is] A still unidentified species.” 
The Hebrew root “גפר” — g-f-r — is associated with brimstone and sulphur.
However, it’s also associated with “ga-far,” a verb meaning “to make thick; to tighten.” The “pi’el” form of that verb means “to make watertight.” “The pi’el is the intensive form of the qal [or root], adding such ideas as ‘much,’ ‘often,’ ‘eagerly’…(etc.)” 
Thus, while we could justifiably translate this as “…an ark of cypress…,” it could be just as appropriate to translate it as: “Make yourself an ark of watertight wood” or even “…a watertight ark…”
“God told Noah to take trees from the area of the Ararat mountains [a]…These are in the east of Turkey toward Baghdad [b]…The wood is very strong and water resistant…Some say this is balsa wood, which is very light and buoyant. [c]” 
“…you shall pitch it inside and out with pitch (וכפרת אתה מבית ומחוץ בכפר).”
The Ark was sealed with pitch.  In Hebrew, “pitch” is “כפר” — k-f-r. In the form of a noun, “ko-fehr” rhymes with “go-fehr,” but of greater note: It’s the same root as “ki-pur” — “atonement;” as in Yom Kipur. What drash — homiletic lesson — might be drawn from the fact that the pitch, or tar, that kept out the flood-waters is linguistically related to “atonement” — which “saves” us from the inevitable consequences of our own actions?
The ark was 300 cubits long by 50 cubits wide by 30 cubits high. 
If a cubit is understood to be 1.5 feet, it would have been:
450 feet long by 75 feet wide by 45 feet (4.5 stories) high.
If a cubit is understood to be 2 feet, it would have been:
600 feet long by 100 feet wide by 60 feet (6 stories) high.
Approximate views of the Ark:
“Figuring a cubit at about 18 inches, the Ark’s displacement would have been over 40,000 tons, or as large as a good-sized modern passenger ship. To the ancients, such dimensions must have evoked a sense of great awe.” 
On the other hand, perhaps it didn’t evoke so much awe — no one (except Og, in an aggadah/midrash) joined Noah.
There are no directions to taper the ark either at the front (as with most boats) and/or at the back. Also — there are no explicit directions to create a rudder and steering mechanism. In fact, once in the Ark, Noah can’t actually see where it’s going at all, let alone steer it. Its only apparent concession to considerations of “sea-worthiness” is that it’s wider than it is high. If its height surpassed its width, it might capsize more easily. So, those observing Noah might actually have thought his preparations pointless and ridiculous. Why create a boat that you can’t steer?
We might think that such design features are to be assumed.
But their absence demonstrates that during the days and nights in the Ark, Noah and his family were completely dependent on G-d. It could almost be an allegory or metaphor for what real faith or prayer are, cognitively speaking: Completely giving up to G-d both control and outcome, as in the hymn “Adon Olam” — “B’ya’do af’kid ru’chi;” I place my soul in His hand/power.
for more info, see:
 Ber./Gen. 6:14
 Musselman, John L.; Figs, Dates, Laurel and Myrrh; p. 113
 Hertz, J.H.; Pentateuch and Haftarahs; p. 26
 Plaut, G.; “The Torah: A Modern Commentary;” p. 59
 Ben-Yehuda/Weinstein [paperback] Dictionary; p. xi
 Culi, Rabbi Yakov; Me’am Lo’ez; Rabbi Aryeh Kaplan, trans.; vol. I, p. 342; © 1977 Moznaim Publishing Corp.; citing
[a] Bereishith Rabbah
[b] Ramban (no further citation provided)
[c] Abarbanel (no further citation provided)
 Ber./Gen. 6:14
 Ber./Gen. 6:15
 Plaut; p. 59