Construction is restarting this week on the third and largest building in the 20 Midtown development in downtown Birmingham.

Revamped plans call for 274 apartments, from studios to three-bedroom units, and at least 38,800 square feet of retail space on the ground floor, said developer Dick Schmalz.

The third building compasses an entire block bordered by 20th Street South and Richard Arrington Jr. Boulevard and Third Avenue South and Second Avenue South.

The 20 Midtown development also includes a 36-unit apartment building anchored by Starbucks, Chipotle Mexican Grill and AT&T. A second 75-unit apartment building is anchored by Publix Super Market. Schmalz of RGS Properties and Scott Bryant of Scott M. Bryant & Co. are developers of the project.

Construction on the third building was slated to start last summer, but it was delayed due to a series of right-of-way vacations and a hiccup in extending sanitary sewer, Schmalz said. The developers also needed time to get their financing in place.

Now, though, the first two buildings in 20Midtown are 100 percent leased, he said.

And, the delay in the project allowed the developers to study the residential market downtown and make "some pretty dynamic changes" to the design and size of the apartment units, Schmalz said.

He said 28 units were added to the third building, and more 400 square feet studios, with separate living and sleeping areas, and three-bedroom units with up to 1,700 square feet of space were added to the mix.

Rents will be comparable the other apartments in 20 Midtown, Schmalz said.

"The third building is going to have something to cater to the entire spectrum," he said.

An amenity deck will be constructed on the fourth floor of the third building. It will feature a massive pool, a putting green, several gas grills, bocce ball, and a fitness center that's both indoors and outdoors.

Due to the height of the ground level, retailers will have an opportunity to add a mezzanine level to their spaces, Schmalz said. He said they are working to finalize some leases on the retail space.

He said pre-leasing on the third building will begin in four to five months. The construction is expected to take 16 to 18 months, but work will be staged to allow some retailers and apartments to open before the entire project is complete.