what is the quickest way to draw a facet on a solid shape?

Hello,

I was trying to quickly cut of a facet on a solid gravestone. I first made the facet by using a loft with 2 sketches. It looks ok, but if you look closely it is not the right shape.

from the sideview the lines must not be parralel but the lines must meet in 1 point.

I tried to use surfaces and it worked for this simple shape. But is the shapes are difficult it takes me to long.

Any idea if surfaces is the only way to do this or is there a much faster way?

using a loft

using surfaces

SolidworksParts And Features