added 11th september 2014 (except sanctum)
There are 6 types of Buildings with their own bonuses and abilities.
Buildings should be valued for upgrade based on a team build. Barracks are strong for damage rogues and warriors. Academy is great for mages only and good for stamina. The new Sanctum building gives health to all players which has its uses.
How cost is calculated is here. Showing each level is on each buildings page. There is also a calc.
Sanctum = 50*level^3*1.25 (round)
Keep = 50*Level^3*1.0
Academy, Barracks = 50*Level^3*0.9
Blacksmith, Bank = 50*Level^3*0.8
To max out all buildings =(50*level^3)*5.65+50*((.5*(level-1)*level)^2)*5.65
Quick answer is it will cost 12,458,250 gold.