How much do I need in cash reserves?

[Lucas Mills]

Do I need enough cash reserves to cover any possible capital expense at the onset? For example, what if the roof goes bad (somehow) a week after buying the property? Or the water heater? Or both? Or are there better alternatives? I've heard you could use a partner, but how might this work? A roof goes bad and you hit your partner up for 10k - how do you pay them back and how do they benefit? They get paid some interest with monthly payments? Just looking for some ideas as to how to approach REI in the wisest, yet most practical way in the beginning.