Is this the best way?

 From:  Cube
Just having a play and was trying to create an object with a variable fillet.
The fillet part i managed fine using dual rail sweeps, but this left the need to build the rest around this, and then fill in the top surface (see pics). In the end I found a few posts and using a combination of instructions; I selected the top 'edge', 'copy and pasted' it and then extruded it out. Next i 'copy and pasted' the same top 'edge' and squashed it 'flat' then extruded it out to intersect the other extrusion. Next i used a 'Boolean Isect' ('Boolean Diff' kept top part and removed the bottom) My question is was the best way to fill the top hole?
I have a feeling this top surface may not be as it seems, if i try to 'Boolean Union' it to the rest it goes a bit odd.