In the current WW Journal "Workshop Projects and Techniques" special edition has plans and an article for a tablesaw outfeed table which lowers to become an assembly table. It clamps to the back of the tablesaw when up and uses a pivot arm to lower. The base has a drawer for additional storage.
I've also seen a simple adjusting height table. I uses 2, rectangular boxes on their side as a base and a torsion box as the top. The short side of the box is your lower height, the taller side is your taller height. To change height, lift up the left and right edges of the top and rotate the bases. The plans for this at home on my PC or in my project folder. If you want it let me know.
Mark