Google parent Alphabet Inc. has legions of Web developers. Soon it might be in need of real-estate developers.

In coming weeks, top executives at the Mountain View, Calif., technology giant are set to weigh a pitch from Alphabet’s urban technology-focused subsidiary, Sidewalk Labs, on a plan to delve into an ambitious new arena: city building.

According to people familiar with Sidewalk’s plans, the division of Alphabet is putting the final touches on a proposal to get into the business of developing giant new districts of housing, offices and retail within existing cities.

The company would seek cities with large swaths of land they want redeveloped—likely economically struggling municipalities grappling with decay—perhaps through a bidding process, the people said. Sidewalk would partner with one or more of those cities to build up the districts, which are envisioned to hold tens of thousands of residents and employees, and to be heavily integrated with technology.

The aim is to create proving grounds for cities of the future, providing a demonstration area for ideas ranging from self-driving cars to more efficient infrastructure for electricity and water delivery, these people said.