:s Importing - Relating Records from Custom Module to the Leads Module

OK please help me figure this out -

I have a custom module (Buildings) I created, I can import data into the module alone.

I have a bunch of leads that own buildings. I have the lead record information with their ID numbers from the crm.

I want to import into my building’s module a list of buildings associated with the lead records (each lead, a different building)

I can see a field for Campaign ID in the import file for leads, but that is the only field I see that could relate a lead with a Campaign and I am not sure how this was programmed. I believe the Campaign has to already exist for this to be used.

As one can import leads and have them associated with a campaign, i would like to import buildings and associate them with a lead.

Can anyone tell me how I can set up a similar field in the import file for Buildings to associate with existing records in leads?