Where to buy a high-end custom-made telescope?

Greetings,

In the course of my architecture practice, I have encountered a client
who wishes to built a personal observatory. Their budget for the
scope itself (nevermind the enclosure and sitework, et cetera) is
$750,000. This seems like an akward number to me -- a lot larger than
any definition of "amateur" that I'm familiar with, but a lot smaller
than any institutional observatory I've ever heard of. Nonetheless,
if you had $750,000 to blow on a telescope, to whom would you go?

Thanks in advance for any help you can give!

Cheers,

Nathan Koren.