with mine i used the height of sitting there so around 32" and then subtracted what i had for plywood and styro and then the legs. 
You can do the flush look or the recessed look too. 
I have huge trim around mine 7.5 " and it accents the wall too and i have a 4" recessed look around the tank.  Look in my journal in Asmodeus 150 in wall.  Than is all what i have ever done. 
		
	
		
		
		
		
			
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				180 starfire front, LPS, millipora  
Doesn't matter how much you have been reading until you take the plunge.  
You don't know as much as you think.
			 
		
		
		
		
	
		
		
	
	
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