Thanks for all the positive comments!
I've seen this exact same idea with fish...I suppose you can put whatever you want in it, but goldfish and Betta's really don't last very long in containers without heaters and filters. It's a very cute idea, but not very animal friendly.
Anyway, I'm finishing the third one now...will edit my first post to add the picture.
Still have one more (it's base coated yellow) with no idea about what to put on it!