JAY-Z Forget Rap ... I Work Construction Now

Jay-Z is keeping a close eye on his multimillion dollar NBA investment -- showing up to a Brooklyn construction site yesterday to check out the future home of the Nets ... and even trying his hand at some hard labor. 

The rapper toured the dirt-filled construction yard on Friday -- known as Barclays Stadium -- to take a gander at where his Brooklyn Nets will earn their stripes ... as in black and white, 'cause the team's colors just changed too. Get over it. 

Oh yeah, we also got video of Jay-Z careening around the construction site on a bulldozer -- reaching breakneck speeds of approximately 1 mph. It's pretty hilarious.