Tap your players creativity. If I already have a rough idea, but no details I would ask the players to fill the gaps, especially in a sandbox game:
[Character-name] you open the door and enter a dark library. Tell us what you see.
You'd be surprised what great ideas the players come up with.
Sorry for not getting back to you.
You're right, offering that creativity to players can be fun. I've tried it in my games though and it's done two things. It's slowed the game down as my players tried to think of things, and it took away their suspension of disbelief because the world became collaborative rather than remaining something steadfast.
I've started asking for their descriptions much more during combat as that is a dynamic environment, but most static locations I reserve as my responsibility to describe.
A large part of my game for my players is my organization. I've given them the feeling that no matter where they go or what they do I have something prepared. The world feels like it is alive and independent of them. While at the same time they can see the changes and impact they make upon it.