My suggestion is to avoid the felt, and go with a smoother cloth. I have had success with canvas, although the master from whom I learned my technique asserts a bed sheet is best. These types of cloth go better over (yes OVER) your terrain elevations, and also provide a better surface for further attaching or coloring (as described below).
Any interesting cloth tidbits can be used for fields … faux fur, some terry cloths or even heavy corduroy cloths. I have also used thin felt, with lines of model RR shrubbery glued down, to make row crops. Popsickle sticks and stirring sticks (from your friendly coffee house) can provide the bases for hedges or lines of trees.
Your local sewing supplies shop can provide many choices. They can also provide a spray adhesive (temporary) which can be used to keep the fields flat on your battleboard.
Then … pastels! You can create all the roads, rough terrain, and forest floors you want with a pack of 20 earth-tone pastels. Even the slopes can use a touch of a different color.
Here is a grounds-eye view of a 1941 Russian village.
Here is another view of the same village, taking in the wooden hill on the near side.
Here is a long view of a Tunisian village in 1943.
Italian forces advance on the village from the south, across the fields of row-crops. Note the seasonal creek on the upper right, which is marked with some green pastel and some crushed stones (RR talus).
A lone Italian field gun overlooks the debacle as the attack is beaten to a stand-still in the approach to the town. This view gives you a sense of the elevations. Note the pastel striping I used to give a highlight to the slopes of the ridge at left.
I have learned this technique from Mark Luther, who posts on many of the wargaming forums including this one. If you get a chance to look over some of his AARs, I strongly recommend it. He is a master of creating superior terrain from re-useable cloth and pastels. You can find one of his recent AARs here: TMP link
-Mark
(aka: Mk 1)