There are quite a few purpose built roller ski tracks now:
In the Vercors at Villard de Lans (a lot of competition skiers train here in the morning like Forcade, Dorin, Weirer sometimes)
In the Bauges at la Feclaz
At the Col de Porte - short loop with biathlon area
However there are the banks of the Isere from the University north to Chambery, either left or right bank and you can skate easily as far as the quais in the center of town.
The Drac on the left bank from Echirolles right the way south past St Egreve
From the Porte de France all the way to St Quentin sur Isere. On the Lyon side of the Isere you have 90 km + of shaded tow paths along the river to skate on. They've redone all the tarmac on the tow paths this winter to remove all the tree roots.
People skate up the Murianette road north of Grenoble - it is very steep though, around 12% in places. I've seen that Victorial Pradal has skated up to the Bastille - but it is 25%!!!https://youtu.be/YnUIyAipzX4
I've skated up to Pipay - it is a 7km road around 6%. You can return via a path in about half an hour on foot, or hitchhike.