Bible Question: how long did it take noah to build the ark?

There is not a direct scripture , except indirectly found in Gen 6:3, stating that the fallen angels were given a 120 years, when you read Gen 6th chapter you will find that is the reason why Noah built the ark.

Noah’s family was singled out as exceptional, in the statement, "Now Noah was "—implying that few or no others were perfectly generated--of pure Adamic stock. (`Genesis 6:9`.) Noah’s family, therefore, included all the uncontaminated--only eight persons. They, by Divine command, built the Ark, and thus witnessed to the world the Divine intention respecting a Deluge while the Ark was being Prepared The disloyal course of the angels apparently continued for centuries without any outward manifestation of God’s ability to check them. Thus all the holy angels we retested, and all who chose "were disobedient in the days of Noah."--`1 Peter 3:20`.

Noah’s message respecting a Divine judgment by a Deluge seemed ridiculous. Until the Deluge there was no rain. The last of the great "rings" which then flooded the Earth was of pure water. For centuries it was spread out over the firmament. The whole Earth was a great hothouse. There were practically no changes of seasons, nor storms, because the great water canopy preserved it in perpetual Summer. Of that period we read: "For as yet there was no rain on the Earth." (`Genesis 2:5.`) Noah, the preacher of righteousness, was mocked and considered a fool because of his faith in God’s Word, just as others of the Lord’s people at various times have been mocked by those who lacked faith, and are yet mocked.

Food for thought Why did Jesus in Matt 24, talk about Noah ? Mat 24:37 But as the days of Noah [were], so shall also the coming of the Son of man be. 24:38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noah entered into the ark, 24:39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.

Did you ever look the meaning of the work coming?
Why the comparison of the days of Noah to the days of Jesus coming?