Ok I have looked at your model. The edges need beveling as you have some very sharp edges that will not look good in a render. You seem to have added edge loops to smooth it? They wont work as it is, I would also just grab the top edge and do an extrude then play with the vertex positions to equalise the plane that you want..
If I get time I will have a look at it over the weekend.
cheers bullet
bullet1968
"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes