The EGCC airport layout in the default apt.dat is very accurate. I would recommend using that instead of trying to make another one. Bear in mind that the runway and taxiway data is stored in an apt.dat, and the building and object data is stored in a dsf file. So, if you want to remake/alter the buildings, you only need to alter the information in the dsf file. Airport buildings generally come from a Custom Scenery package, so have a look in your Custom Scenery folder for a scenery with Manchester Intl in it. If you remove the sceneries for Manchester from your X-Plane folder, you should be able to load X-Plane again and find nothing but runways and taxiways there. These will be from the default apt.dat. Its possible that you might have some X-Plane style building derived from OSM data being placed there if you load the sim without any Custom Scenery. Without screenshots its hard to know what you are seeing. If after removing all custom scenery for Manchester from your X-Plane folder you still have buildings there, try making an exclusion zone in WED or Overlay editor to exclude objects from that area. There are lots of useful posts about the use of exclusion zones floating around online, but let us know if you need some more help, and try to post a few screenshots to show us what you are seeing.