The second building is a parking pedestal with two residential towers on top and also containing significant retail space. The pedestal would be lined with terraced residential units on the riverfront and on its main street, Northwest North River Drive.

The buildings would be separated by a long breezeway connecting North River Drive to the planned river walk. The breezeway would be lined on both sides with retail. The plans show a lushly landscaped, boardwalk-style river walk that Hellinger said would be modeled after New York’s famed High Line, an elevated park on a former rail line, to encourage visitors to stroll and lounge by the river. The developer is also talking to Miami-Dade County about taking control of a smaller, publicly owned abutting parcel to the east, now part vacant land and part parking lot, that could be used to extend the project’s river walk and green space. The proposal’s extensive retail component, which Hellinger put at 475,000 square feet, makes it “a real improvement’’ over the previously approved residential-only project, said James Murley, a member of the Miami River Commission, an advisory group that reviews new development along the waterway to ensure it complies with the greenway plan and is compatible with surrounding areas. The comment came during a public meeting Friday between the developers and members of two commission subcommittees.

Hellinger told commission members he is making “considerable’’ revisions to his initial plans, submitted to the city planning department in January, in response to comments from reviewers and river commission members. Those include moving loading and auto drop-off areas away from the river walk and into interior areas.

City planners have also objected to the retail building’s largely windowless design, which shows its riverfront facade covered by textured cast-concrete panels, and the project’s overall blockiness. Reviewers also concluded the passageway between the two buildings is too narrow.

While praising the river walk design as “beautiful,’’ assistant city planning director Carmen Sanchez said in an interview that she has asked Hellinger and his architects, ADD Inc. of Coral Gables, for “refinements’’ to the building designs. “They were very receptive,’’ Sanchez said.

In an interview, Hellinger’s retail consultant, Roger LeBlanc, said the plan calls for the first floor of the retail building to be anchored by a grocery store on one side. The riverfront side would feature four or five restaurants with outdoor seating. The next three levels would feature four or five big-box retailers. LeBlanc said he already has several signed letters of intent, but declined to provide any names.

The type of tenants the project is going after is believed to include the likes of Marshall’s, TJ Maxx, Homegoods, Bed Bath & Beyond, Sports Authority, Michael’s and Ross Dress for Less. The fifth floor’s main tenant would be a health club, and the sixth floor would feature one or two furniture stores.

But the challenge is convincing retailers to deviate from their typical format. While retailers are starting to do more vertical retail in urban markets like Miami-Dade, this project would be taller than anything else that has been built.

Hellinger does not believe that’s going to be an obstacle. “If you want to be in the urban core, you have to start thinking vertically,” he said. “We have more interest in our project than available space.”

Hellinger said he is currently funding the project himself with individual private investors, most of whom are international. When construction is ready to begin he expects to secure traditional bank financing.

The plan must undergo a series of public hearings at the river commission, the city’s design-review and planning boards, as well as the city commission. Hellinger said he hopes that final vote will take place by May.