Jason, do you have access to one of those laser levels? 
The one I am thinking of shoots a red horizontal line on the wall.  
If you use one of these you could set it up so that you measure up to the line on all 4 corners and the middle to check for level. A lot more accurate than a bubble level. 
I have access to one, if need be PM me 
Dietmar 
		
	
		
		
		
		
		
	
		
		
	
	
	 |