Oooer ???

No, nothing to do with the bgl. You don't change anything like that.

Get hold of Airport for Windows version 3 (or Flight Simulator Scenery Creator which I used to prefer but now don't) and Easy Object Designer (EOD, much easier than GMax and you can still use it for all versions up to FS9).

Do the tutorials that come with em - there's NO shortcut. Learn about excludes that can be placed so precisely you can take out individual buildings. Learn about areas, flattens, polygons and how to make custom buildings and objects using EOD and how to place them in your scenery using Airport or FSSC. Learn how to add water, new roads, taxiways, aprons using the many design progs that are now available. Get hold of AFCAD 2 and see how that can now be used to add/modify taxiways, parking, aprons and stuff.

If you want to start in a much less ambitious way, get hold of my MakeScene package and start dropping 'default' objects into your scenery in minutes.

You see, like most things to do with FS there's a learning curve - too much for most people who just want to download stuff other people have made and fly.

But if you're one of the small minority, and the fact you've asked might suggest you are, you'll find that if you can stay with it on that learning curve, making and modifying scenery is great fun and something that adds another amazing dimension to your flightsim experience. Like a lot of us, you'll probably find you  spend more time designing than you do flying

Go on - give it a go

Roger