Are Schedule E expenses commensurate with ownership percentage? Or based on how much an individual actually pays?

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Own a rental property (single family home) with other individuals.   For some time now we have been paying for all costs, including those for "improvements," commensurate with our ownership percentage, and each owner reports this on Schedule E of their individual 1040 returns.  

How would we go about reporting things if for example one owner were to pick up the entire tab for a big a expense (e.g., major repair)?  What about for a big improvement (e.g., new roof)?