Miami’s roller coaster real estate market is booming again after its worst crash left dozens of unfinished buildings and failed condo projects.

Related Group of Florida, Adler Group and Area Property Partners LP, are among builders developing amid a shortage of rental properties as the economy improves. The average rent for a two-bedroom apartment in Miami increased 6% to $2,568 a month in the third quarter, compared with Q3 2011, according to Condo Vultures, a brokerage and consulting firm.

“There’s a boom in Miami that we’ve never seen before,” said Stephen Ross, chairman and founder of New York-based Related Cos. and owner of the Miami Dolphins football team, at the Bloomberg Commercial Real Estate Conference in New York. “ Miami is probably the hottest real estate market in the US from a residential perspective.”

With most of the unsold, unoccupied condo towers that dominated the Miami skyline as recently as two years ago converted to rentals, the number of multi-family developments is soaring, with one research firm estimated that as many as 3,000 new rental units will be added each year from now to 2015.