$625 Million PowerBall

[Keepswiming]

I would build a floating house over a reef, with a downstairs that’s all glass and underwater!

 

[Rick.45cal]

If I won that much I’d build my house at the bottom of my reef aquarium!

 

[Sod Buster]

If I was handed that much cash, nobody would see or hear from this boy again. I'd do swiss family robinson, just with my own airstrip.

 

[PaulPerger]

I figured since I asked I ought to answer...

I would build a few tanks. One very large peninsula (10' x 6' x 4') tank which would not be coral heavy, but large, beautiful fish heavy. I would also do a large reef tank with a bunch of small beautiful fish. I would probably also fo a few specialty tanks. A nem and clown harem, and a garden eel tank. And, of course, an incredible fish room to support them all.