I have no idea I'm not moving for a few months so I haven't begun seriously looking. But wanted to get a feel for what everyone thought. There is a 150 at my LFS that is six feet long but I'm unsure of the height.
Well, the standard dims are 5x2x2 for 150g, 6x2x2 for 180g
Of course now days we have more choices as some people prefer more shallow than 24"(24" is the sweet spot for me personally w/ what I keep, something you should think about, what's going in this)
Also lately many are going 30" or more front to back, nice if you have room for that, and can get to back of tank or reach that far.
Maintenance and what I keep are my key factors
I would sit back, think about what you MUST have in this tank as animals go, build to fit their needs as well as yours.
Do you need a sand bed?
Do you want decent size tangs?
What corals, and what lighting will they need? What type of lights do you have a budget for, what kind of depth/penetration do you need?
Do your lights fit canopy, or cover the spread?
FWIW, I've had 2x180's, and 2x 150's, all were good, but 180 is right about my personal favorite for most everything I wish to keep.