@UngulateNerd92 Not very large if they want to keep the hornbills flighted, the undoing of which presumably would be required if they wanted to keep them in an open exhibit.
I don't think they are at all suitable for the savanna aviary as that aviary also houses smaller species like doves and starlings, smaller hornbills et cetera.
And they tried at one point adding them to the aviary with the marabous and vultures, but that seems to not have worked out. That aviary would be the most suitable perhaps, but if they don't get along there that is not an option anymore.
If something new were to have to be constructed for the hornbills, I don't see it happening at Antwerp. Perhaps at Planckendael, were they would be a nice addition.