Another way, and perhaps a little quicker would be to create a poly plane with 8x8 subdivisions. Then delete the faces you don't want. Then just select the object and extrude to the thickness you want. EDIT: SELECT ALL THE REMAINING FACES AND EXTRUDE IS WHAT I MEANT TO SAY.
As jsprogg mentioned, there are several different ways to model things and this is just another way.
Don't be satisfied with what you can do but rather strive to do the things you can't do!
Exceed Expectations!