If you have 2 weeks in Morocco, do the full loop in one direction: the imperial north first, then the Sahara, then the south, then Marrakech and the Atlantic. Casablanca in, Casablanca out. It is the route we build more than any other, and the one our 13- and 15-day journeys are based on.
The order matters. From Fes the desert is reached by one road, south through the Middle Atlas and the Ziz valley to Merzouga. From Merzouga you roll west through the gorges to Ait Ben Haddou and over the Tizi n'Tichka pass to Marrakech. No backtracking, no direct Fes-to-Ouarzazate leg that looks short on a map and is not, and no zig-zag from Marrakech back to Fes.