Currently, we do not offer individual files for buildings. It is on our roadmap, but until we have a solution that works for all software, we are only able to deliver full kits as a single file.
For software that requires buildings to be imported individually, there is a simple work around using Blender (www.blender.org) which you can download for free.
Download the Blender Native file of your kit
Open the kit in Blender
Select the model you'd like to export
Go to File ->Export -> FBX (Please note, there is a checkbox in the bottom left of the export window for exporting the Selection Only.)
For Element 3d users, you can find the recommended settings for exporting individual models here. All of our world kits are already broken up by material, so following these guidelines, you shouldn't have any trouble with applying multiple materials per building.