Alex Rodriguez just doubled his chances of being your next landlord with a second Big Apple apartment building purchase.

A-Rod, who bought his first NYC residential building with “Shark Tank” TV judge Barbara Corcoran, is in contract to buy a 114-unit brick apartment house at 340 E. 51 St., The Post has learned.

The former Yankee slugger and his new investment partners paid “less than $100 million” for the 14-story Turtle Bay building, known as “The Allen House,” where rent for 423-square-foot studio apartments costs $2,550 a month, according to StreetEasy.

The plan is to spruce up the place, including a gym, which will allow for higher rents on fair market units, Rodriguez’s partner, Ofer Yardeni of Stonehenge NYC, told The Post.

As apartments are vacated they will also be upgraded, including electrical service, flooring and stainless steel washers and dryers in every unit. “You can do it since over 90 percent of the units are at fair market rents,” which creates natural turnover, Yardeni said.

In buildings with a majority of rent-regulated units, there is less vacancy and less incentive for landlords to make upgrades because they are capped on what they can charge in return for their investments.

The investing trio, which also includes brokerage guru Adam Modlin of the Modlin Group, will rebrand the building with the Stonehenge name. The partners also will introduce a new concept for some units dubbed “Stonehenge Flex,” which Yardeni described as “sexy and cool” furnished units that will come with cleaning services targeted to young professionals who can walk to work.

These units will offer six-month leases. “We will take it to a completely different level,” he said.

Rodriguez, who is engaged to “Hustlers” star Jennifer Lopez, already owns more than 15,000 apartments in 13 states through his Monument Capital Management. He first dipped his toe into the New York City real estate market in June after meeting Corcoran on ABC’s “Shark Tank” and chipping in to buy a small East Village building.

The Post later revealed that Rodriguez’s A-Rod Corp. had teamed up with Yardeni and Modlin for bigger real estate deals.

Brokers Paul Liebowitz and David Krantz of Savills brought them the deal.

“There was no set up and no information. I needed to send my team to do the due diligence and move like a Navy Seal,” said Yardeni a former Israeli army officer.

As for A-Rod, Yardeni says he’s been a great partner. “He prepares for real estate deals the way he prepared for a baseball game. I feel like I’m playing for the Yankees.”