Purchasing apartment: cash reserve

[Sam Lee]

I have yet to purchase an apartment building but I want to know how much cash reserve you need when you first buy the building, and then when you are running it. Let's say the downpayment (20%) is $100k, how much would you generally need behind that in cash reserve?

an extra 20K? 50k? or maybe % would be more helpful

I want to know because I estimate saving a certain sum by XX year for the downpayment, but I may need to save more depending on the cash reserve

Thanks!