If it'll be "real hard to clean" why would you put a betTa in there?
That's what she means, I think.
Here's the thing: people come up with all sorts of kooky novelty tank ideas all the time (remember goldfish in the heels of platform shoes? There's also someone else on another board who wants to turn an overpriced Pottery Barn glass vase-bottomed table lamp into a nano right now too)...
...I think people fly off in flights of fancy and tend to go a little amok when it comes to designing tanks because they do excite our sense of wonder and creativity. However, just because you can
stick a fish in it doesn't always mean you should
. Snails and even shrimp have very small biological 'footprints', but fish are much messier by comparison: they excrete far more waste than either of the former two.
Would you want to be locked in a tiny circular room with your own poop? Would anybody besides R. Kelly?
IMO it'd be a better idea to start w/ a planted tank, possibly a couple inverts as mentioned, and go from there. Personally I think some reddish plants would make that thing look amazing. One more little consideration too - when this thing is filled more than halfway with water, it'll be easier to tip or roll too. You should consider some kind of support or brace for the bottom.