Seems difficult? Constructing wrap trousers has never been so easy!
All you need is basic trousers pattern.
Then use Flipping objects by line instrument.
Just flip the point of the central dart along the bunt line.
Use Point intersect line and axis instrument to draw a wrap sketch line.
Flip the upper edge along the wrap line.
Finally use Rotate objects instrument.
And rotate upper edge, bunt and inseam line over the lower point of the wrap sketch line.
Draw all missing lines and curves.
Enjoy your pattern!