Alan. The conventional Freeware scenery design applications will do much the same as LAGO's Scenery Enhancer product & much more besides. They might not be so easy to use & you will have to go through the usual learning curve. These programs are also posted here at SimV but I'll give you the link to their home sites for the latest versions. I suggest you try both to see which one suits you. I find FSSC easier to understand & use.
Airport for Windows.
http://www.airportforwindows.com/FS Scenery Creator.
http://fssc.avsim.net/Both are capable of importing the API macros which are posted here & on various FS sites. These are 3D scenery objects including hangars & buildings which can be dropped into an existing location or used for creating a completely new airport. The possibilities are almost unlimited.
You can also create your own API macros with EOD.
http://www.echos.ch/eod/PS. All the above are under constant development. They should be compatible with FS2004 but there might still be some improvements yet to be addressed. The main problem with all these 3rd party programs is that M$ seem reluctant to release the promised SDKs.