If you type "Hamster Detolf" into google and click on "Images" you will see loads of set ups! I've done that particular search a few times.
If it was me, with all that space, I'd get a labyrinth house (or make one). Our current and last Syrians have both loved having a labyrinth house. The litter tray is inside it and they use it. The flat roof can also double up as a platform.
I would definitely put a platform in it somewhere. Something for them to sit under for shelter, and climb up onto. And I'm a fan of the large cork logs - interesting texture to climb over and a nice big dark tunnel to run through.
Your main decision might be the wheel
Not all wheels will fit in the detolf with a lid. Most 11" wheels will but the 12" silent runner won't if it's on its stand. But you could use the mounting plates and drill a hole in one end of the detolf and mount it that way possibly (I'm not actually sure if that works).