"The comment I hear most from my friends is: 'I didn't realize it was going to be that tall,' " Roger Gregory said, walking through the 40-story luxury residential building his company is developing at the northeast corner of Weslayan and West Alabama.

The city's tallest apartment building, now occupied by hard-hatted construction workers, will be home to well-heeled Houstonians when it's completed in the spring. The first residents move in this fall.

Soaring from a relatively flat Houston landscape near the tony River Oaks neighborhood, the building offers expansive views that get more striking - and expensive - with each floor.

The average unit will rent for close to $4,000 a month.

The developer has been quietly accepting leases and just last week opened a marketing trailer next to the site.

Thirteen units already are spoken for, including three 4,000-square-foot penthouses that will lease in the $12,000 to $13,000 range.

"Some of our people are coming from other penthouses. They've been there for years, and they just want something newer. They want a change," leasing agent Misty Meredith said.

The smallest apartment in the building has 680 square feet, but there's only one, and it's already leased. In fact, three people were vying for the unit, Meredith said.

As the booming energy business and generally strong Houston economy continue to bring well-paid employees to this area, the builder doesn't anticipate a lengthy lease-up period.

More than 400 prospects have already contacted the company seeking information through a website launched about 45 days ago.

Houston-based PM Realty Group is developing the tower, called 2929 Weslayan, its third high-rise multifamily project. The other two are in Dallas.

Each unit will have one of 14 design and color schemes with walk-in closets, granite counters and wood floors. All will have built-in speakers and a smart entertainment system allowing residents to control temperature, lights and other features from a mobile phone.

The eighth floor will house tenant amenities, each with a unique view.

The gym will overlook the Galleria area and Greenway Plaza, while a "sky lounge" and fire pit will have downtown views.

A saltwater swimming pool, however, will be shielded from the city by extensive landscaping and cabanas, an intentional design feature meant to "provide an oasis," said Gregory, president of investments for PM Realty Group.

Baltimore-based RTKL designed the structure, which will have 254 units averaging 1,500 square feet. Many will have three bedrooms.

When the building was announced less than two years ago, the design firm said the inspiration came from "the flow and sophistication of an evening gown." The tower has balconies that seem to taper as they move up the building.

The project will have about 12,000 square feet of retail space on the ground floor.

Local and national restaurant groups are considering taking some of that space, said Gregory, noting a Japanese restaurant from San Francisco and a couple of groups from Dallas who are interested.