du yu meen roof top is up 2.8 ft & distans from eev tu senterline is 8.6???????.... yu shood no, bilding trades sae thats a rise av 2.8 & run av 8.6... so slope=2.8/8.6=0.32558... =32.6%..... but me spekt yu want math-man anser insted.... tan(slope)=0.325581395, so angel=18.0342855 deg.... thats not nuf....make it steeper