Measure the top of the egress window well. Make a small drawing of the well, noting the measurements on it. Make your cap at least one inch larger on three sides of the well so it covers the well entirely.
Lay out your grate. The grate acts as the basic cap over your well. If the grate isn't sized for your well, cut it to size with a hacksaw. For additional protection, and to keep leaves and debris from falling into your well, you can glue a piece of plexiglass over the top of the grate, or wrap the grate in fine mesh.
Place the grate over the top of the egress well and check for gaps. Once the grate is in place, attach a hinge to the well wall and the grate. The hinge, or multiple hinges if you want to add additional strength, must allow the grate to be pushed up so a person can climb out of the well.
Exit through the egress window. Oil the hinges for ease of use.