From FlightGear wiki
Where can I download additional scenery?
How do I install scenery?
Why do I only see water when I start at a location?
You've forgotten to download the scenery for this part of the world, or you haven't installed it correctly.
How do I place objects, like buildings, into FlightGear?
- You can use the UFO or place them manually.
- You can use the tool "fgopt" (object placement tool) to modify objects that are already in in stg file
- You can place Project3000 and other objects with WED
Why do I get a red hue instead of textures?
There are several reasons for this.
- You didn't have the texture files in the same folder as the .ac file.
- The dimensions of your texture image file aren't powers of two. Like: 286x120, 530x88 etc.
- Your texture isn't exported to a format supported by FlightGear. .png and .rgb are used for the majority of textures. You can convert textures with a free software called Gimp (Gimp).
Where can I upload my buildings so other users can download them?
Send all your buildings to the FlightGear Scenery Objects Database.