well the difficulty in making it would be the perspective you chose to go with. You could just boot up your vr and run it on steam and use a vr like a desktop (I wouldn't really consider this a vr experience)
next would be to make it top down like Ardanian Kingdom which would probably be the cheaper option that's still a vr experience.
or 2d graphics that wrap around you with options and a small number of actual 3d objects, this would probably do best that
Alternatively Skyrim VR... which is self explanatory but you'd be starting from scratch to make a 3d environment.