Would this be safe/okay?

Consider those vents don't blow air straight up but rather to the sides I think it will be fine to put the cage over top of it.

You could also use a product like this to redirect the air from the vent:

Floor Register Extension - Furnace/Registers - Heating & Cooling - Indoor Living - Improvements Catalog

Seeing as you have the cage raised off the floor by one cube and the bottom is chloroplast, it should be fine. The problem is when things are more directly on top of them. Not that I know too much about it, despite my dad having a whole lecture about 'air flow' and other foolishness. He would never let me close my bedroom door since the thermostat was in there.

The bottom of my cage isnt actually coroplast, its just plastic-like the plastic you lay down to paint. I think I'm gonna go ahead and expand it...I'm gonna check with my dad first though so that I wont get it finished and then have him come and flip out over the vent having something over it (I can see him doing that) My room has another vent though and my bathroom (attached to my room) also has one, so I dont see why it would matter. My room is always the warmest room in the house anyway.

Jenni_Feathers said:

My room has another vent though and my bathroom (attached to my room) also has one, so I dont see why it would matter. My room is always the warmest room in the house anyway.

Click to expand...

With your dad's permission, then, you might be able to close off the vent in question.

Good luck with it!