Contract integration with real estate

Hello,

I need to create a maintenance contract,

It's a year long contract for lifts maintenance, with monthly rent. The contract must be associated with a building created by the real estate guys.

I know i need to create a basic contract (me31k). I choose the vendor, wk type of contract, and put the organizational data.

Then i choose the validity of the contract, and the value.

On the next tab, i set the item category for D (services), and K for the accounting and all, but i need somewhere to assign it the offices created by real estate.

I only know these are a cost object.

So if anyone could guide me through the necessary steps i would be very grateful.

Thanks