The whole sequence of events in Genesis chapters 6 - 9 illustrates one of the most important lessons for mankind today:  the recognition of God's Sovereignty and the acceptance of our (man's) responsibility.  Both are vital to the happy relationship between the creature and the Creator.  Never does God's Sovereignty negate my responsibility, nor should my sense of responsibility override His sovereign Will for my life.  If they remain parallel and in the correct relationship, all is well.  If divergence or convergence occurs, it's a recipe for disaster!

God decided that the end of mankind must come.  He chose the timing and picked His servant from an estimated three billion people alive at the time.  He calculated how long it would take Noah to fell the trees, prepare the lumber and construct the vessel on the stocks.  It still left time for Noah to continue to preach righteousness in public, while his sons continued with the work.

He tested the faith of His servant before the arrival of his first-born, Japheth in 1556 AM (Anno mundi - In the Year of the World).  Noah may have had to wait another twenty years or so before the three sons were fit for such heavy labour.  Shem was born two years later in 1558AM.  For most of this period, he could consult with Lamech, who did not see the last five years of shipbuilding, and Methuselah, who died in the Year of the Flood.
 

There is no mention of metal in these chapters:  wood dominates the scene.  The Hebrew word  gophar, may indicate hand-tooled timber but the Rabbis are not agree upon this rendering.  It certainly wasn't balsa wood as mentioned in the legends of some South Sea Islanders and their tribal account of the Flood.  It had to be strong, durable and yet able to be fashioned by human tools.  Wood joints were necessary - perhaps Noah invented the scarf-joint and trenails.  At least the ancient Egyptians who moved away from the Tower (Ziggurat?) of Babel used them in the Nile boats, a few hundred years later.  The controversial water-proofing liquid called "pitch" in the Authorized Version was the vital ingredient.  But the translators changed the meaning to suit their 17th Century audiences who would easily recall galleons, beached on the shore, being scraped and then coated with tar (pitch).  But the word chosen by the Holy Spirit of God is not "bitumen" but simply "covering".  This links immediately with the rest of the Pentateuch in explaining the need for atonement by the shedding of sacrificial blood on the altar.  One tough coating called "shellac" could have been the basis; today, it is harvested in India; the insects' blood is mixed with its waxy secretions.
 

Experts disagree as to the value of the Hebrew "cubit"; some say that it is approximately 17.5 inches but there is also a longer "cubit" as recorded in Ezekial 40:5.  Other ancient measurements varied from 17 to 24 inches.  Most Biblical commentators regard 18 inches as the Biblical cubit.  From the vessel-design point of view, the ratio is the vital factor:  a length of six times the breadth (beam).  The God-given dimensions of 300 cubits x 50 wide x 30 high, gave a capacity of around 1,400,000 cubic feet.  We are told how the spacing of the three decks was allocated:  the lower deck may have been reserved for heavier animals such as dinosaurs, with food, living quarters and the birds on the top deck.  Was the single Great Door the only entrance?  Did flying bats, birds and Pteranodon all use the same way in?  If so, the, the Door would be a type of Christ as the only means of entry into relationship with God for fallen creatures.  To answer to the Divine requirements most easily, Noah would have built a box-shaped boat, designed to float as a barge.  No means of propulsion were mentioned:  no masts, sails, oars or rudder.  Some of the Kurdish reports on the finding of Ark remains on Mt. Ararat during the past century and a half, mention slight flaring of the hull sides, bows and sterns, i.e. they sloped outwards at the top.  The well-known painting by Elfred Lee was produced from the instructions of an eye-witness who had climbed the mountain.  The "window" on top has also been reported by several mountaineers.  The precise meaning of  "...in a cubit shalt thou finish it above" (Genesis 6:16) is not clear.  It is possible that this feature was to assist with ventilation and the removal of excess carbon dioxide produced by thousands of hibernating or aestivating animals in the cages (Hebrew "nests") below decks.

Colonel Alexander Koor (1891-1971) witnessed the discoveries of the 1917 Tsarist Expeditions, just before the Russian Revolution.  He later escaped across the Bering Strait and lived in San Francisco until his death.  Koor reported that the interior of the Ark was mapped, described and photographed as far as the defrosting had gone that July and August.  The documentary evidence was captured by the Bolsheviks but it has not been unearthed since the collapse of the USSR.
 

Noah was instructed to make "rooms" or cages for the animals.  Obviously, this was not the only storage because a large variety of foodstuffs had to be stockpiled aboard.  Verse 21 or Genesis chapter 5 indicates that God knew the wide general knowledge of the boat builder who knew exactly what every kind of animal ate.  God had chosen the right man for the job.  The Hebrew words used in verse 21 show that clearly and, in the case of the food stores, Noah had to organise and transport them to the boat.  In the case of the animals moving towards the Great Door, this was entirely in God's hands:  the family was already inside waiting for them.
 

A Holy God has the right to judge evil men.  Society on Earth before the Flood was clearly getting unbearably murderous.  God stated that, "His Spirit would not always strive with man..." (Gen. 6:3), but a way of escape was provided.  Christ is today our Ark of Safety.  We are sheltered from Divine Judgement by the payment of the cost, His precious blood having been shed:  "Without the shedding of blood, there is no remission." (Hebrews 9:22).  The Ark's timbers were impervious to the action of the waters:  The barge floated for 150 days and all emerged alive at the end of the ordeal (375 days).  All the promises of God concerning this event were fulfilled:  we too will emerge onto a new scene when God deals with the final rebellion of mankind against Himself.  There will be a "new heavens and Earth wherein will dwell righteousness" (2 Peter 3:13).  Time for repentance runs out eventually, as it did when the Great Door was closed by Unseen Hands.  The Divine timetable was kept to the minute, as it was when Jesus said, "It is finished." (John 19:30).