300 South Tryon in Charlotte has been topped out for a while is just about finished construction.
Which I think means the tallest under construction in North Carolina will now be the 588+ foot tall, 33-story office building by Lincoln Harris on the site of the old Charlotte Observer building. It is already on the 3rd or 4th floor of construction:
Source
The tallest u/c in Durham is 27 floor One City Center:
And the tallest u/c in Raleigh is the 17 floor The Dillon:
Asheville's tallest is getting remodeled, and I don't know of anything over 10 going up right now in Winston-Salem or Greensboro. Charlotte has a couple more in the 10 to 20 range starting or about to start construction as does Raleigh.