"I... don't actually know?  I would guess some mixture of ultralight materials like... I don't know the English word, moderatel hard waterproof stuff that weighs nearly as much as air, or even less if you fill it with hydrogen though I'm not sure it's stable in that form... and maybe a lot of internal bracing with stronger ultralight materials?  Nearby towers and cable points?  Sorry, I'm not actually a megascale engineer."

"I... don't actually know?  I would guess some mixture of ultralight materials like... I don't know the English word, moderately hard waterproof stuff that weighs nearly as much as air, or even less if you fill it with hydrogen though I'm not sure it's stable in that form... and maybe a lot of internal bracing with stronger ultralight materials?  Nearby towers and cable points?  Sorry, I'm not actually a megascale engineer."

"I... don't actually know?  I would guess some mixture of ultralight materials like... I don't know the English word, moderately hard waterproof stuff that weighs nearly as much as air, or even less if you fill it with hydrogen though I doubt it's stable in that form... and maybe a lot of internal bracing with stronger ultralight materials?  Nearby towers and cable points?  Sorry, I'm not actually a megascale engineer."

"I... don't actually know?  I would guess some mixture of ultralight materials like... I don't know the English word, moderately hard waterproof stuff that weighs nearly as little as air, or even less if you fill it with hydrogen though I doubt it's stable in that form... and maybe a lot of internal bracing with stronger ultralight materials?  Nearby towers and cable points?  Sorry, I'm not actually a megascale engineer."