Scenery objects like aircraft must first be designed using a compatible design tool like gmax or FSDS.  The SDK's tell you how to name parts and export your creations to interface and work in the sim.  A good overview of the design world and flow would be helpful and I can't do that for scenery.  There should be some good scenery object examples in the SDK and it should explain how to build, texture, and place objects in the sim using coordinates.

There are some nice scenery design forums around and it would be helpful to get there and post your questions.  Here are two:
http://www.aerodynamika.com/cgi-bin/yabb/YaBB.cgi?board=Scenery

http://www.fsdeveloper.com/