As a builder of custom chastity devices (among other things), I can see what you're after, but there are technical difficulties. Most male chastity devices are made to be worn long term: that's the point. Now a device big enough to have room for an erection would, as Ozme says, be a bit bulky, and besides, if it held your cock permanently in an erect position you wouldn't be able to urinate. So it would have to be not only big but articulated, And solid, because a cock-cage wouldn't stop you teasing your erection.

So, it could be done - I could make one to those specifications - but I don't really think a CB is what you're after.