Does zakat become obligatory on a plot of land that a person has owned for a long time, intending to sell it to complete building a house elsewhere and purchase new land, with the possibility of changing the intention to invest in it and build a house on it without the intention of living in it?

Zakat is not obligatory on trade goods except with an intention concurrent with possession. So, if the original intention was for personal use and then for trade, Zakat is not obligatory. If it was intended for trade and then for personal use, it ceases to be obligatory. Therefore, selling an item with the intention of getting rid of it or due to a lack of desire for it does not make it a trade good on which Zakat is obligatory.