You could call it a roof. Or perhaps an armilla?
If you were going to get all hard SF about it, a rigid shell around a planet (or indeed around a star) wouldn't be stable, and would indeed fall onto the planet unless it was perfectly centered on the planet's center of mass as @RichardTingle suggests. If it were as low as the ISS, I doubt it could last a week without some kind of (huge) thrusters to keep it in place.
A ring is OK because each part of the ring is in orbit. But as you start to widen the ring, the edges are not in orbit-- they're moving too slowly and in the wrong direction for their altitude, which means they're pulling on the rest of the ring, and it would be nearly impossible to balance those forces.
However, an airtight sphere could be supported by air pressure, and have tethers/struts connecting it to the planet. Those wouldn't have to support the weight, they'd just be to stop it drifting around. Could be a good source of cover artwork...