Saw your reply earlier but didn't have the time to reply then. I see you added SBuilder to the list. That is what you use to create the new grass area. From your list I assume you're designing for FS2004.
Sbuilder-make sure you have the latest version. Click Help>About and should be Version 2.05 Revision 06. If not, you can download the latest version here-
http://www.fsdeveloper.com/forum/downloads.php?do=file&id=68KCLT.zipYou'll need to create 2 polygons to define the new grass area. You'll create them one on top of the other but leave at least part of an edge on the lower one exposed so you can easily get at it to edit if necessary.
1) an LWM-Flatten with an 'all points' altitude of 227.99M
2) a VTP2-filled with the a landclass (bullet next to Classes-click in Classes input line to open Landclass selection window). 095-Grasslands or 096-Grasslands fit nicely.
If you need any further help, just holler.
Dave
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.