Let me count the ways:1) Licensing and Entity Set Up2) Establishing Proper Bank Accounts3) Creating a Phone System 4) Having no PM education or experience5) Accounting6) Marketing - Of themselves and the homes they manage7) Application handling with screening8) Lease execution - minimal understanding of how to fill in a lease9) Tenant laws and regulations10) Tenant relations11) Maintenance (I should say that 5 times)12) Make Ready issues13) Security Deposit Itemizations (the most expensive failure you can quantify)14) Failing to seek advice or education 15) Service Animals16) Fair HousingI could go on, but one of the biggest and would considered the "umbrella".....is not providing a quality service to their owners and tenants. 

Flat roof repairs - are they more expensive than traditional single family house style roofs?

Some realtors try and use the traditional 6-7% cap rates when pricing, but these units tend to sit on the market for months and end up being bought by seminar grads and rookie investors.Also Mary if you are interested in units from 2-8 here in KWC, I would be happy to send you a couple listings to look over and analyze for investment purposes, give you a feel for the numbers.

If you can't afford the down payment, what will happen when you a big cap ex item arises? 

It's clearly a buy and hold but are you trying something creative or the more traditional bank loan route, the best way to get a good answer to any question is to be specific about what you mean. 

Max LTV on a Heloc is usually 90% a a traditional bank.

Especially if the tenants have small children, you have to clearly communicate what items are forbidden to go down the toilets (baby wipes, bleach cleaners, etc) and let the tenants know if they plug the system they are responsible for having it cleaned out/pumped. 

Okay, I guess one of the questions I have is can you combine a heloc and a traditional mortgage, or is there a different type of product for this? 

The trade off of them taking the "risk" to refinance you within 6 months is the rates, terms, etc. will not be as favorable as a traditional lender.

However if you were cash rich and didn't trust the banking system (like some people) and wanted to get traditional financing but also had the "cash" necessary for a purchase.