How do you document/establish the tax basis for your properties?

[Brad Thomas]

I bought my 9th property (a five-unit apt building) about a year and a half ago. All of my previous properties were basically self-sustaining after I put in the initial contribution for purchase. So all bills were paid out of the account attached to the property. But this last property needed a lot of work and only had one tenant, so, even though the property is owned by an LLC, that LLC didn't have much money. So I kept paying for stuff with my personal funds. I have everything documented, but I'm trying to find the best way to establish a clear (tax) basis for the LLC. Should I have the LLC write me a check for all the expenses I've paid over the last year and a half and then write a check back to the LLC as an official contribution (the LLC still needs funds)? Or can I just say I've spent $X over the last year and a half and add that total to the basis?