Buying Apartment Buildings

After having bought so many single family properties I think the next logical step is to buy an apartment building. If bought correctly, an apartment building can provide good cashflow apart from the usual appreciation.

Since I don't know anything about this I've been reading some really good books. Two that are really good are
How to Buy and Sell Apartment Buildings and
How to Manage Residential Property for Maximum Cash Flow and Resale Value.

Anybody know any other good ones?