SAN JOSE — The builders of a new office and retail building in downtown San Jose aim to take advantage of the sun-swept climes of the Bay Area by adding a big rooftop cocktail lounge to the project.

“This is a really cool addition to our project,” said Erik Hayden, managing partner and founder of Urban Catalyst, a development and investment firm. “We believe it will be the largest rooftop bar in Silicon Valley.”

The project is being envisioned for the site of the one-time Lido nightclub and would add offices, a restaurant, retail, and the lounge on the roof of the new structure.

In May, Urban Catalyst paid $6.9 million for the property, which has addresses of 26 and 30 S. First St. in downtown San Jose.

San Jose-based Urban Catalyst was formed to create funds and launch projects that can take advantage of the tax benefits created by opportunity zones in areas such as downtown San Jose and Oakland. Urban Community, a firm led by developer Gary Dillabough, has an equity interest in the project, which is expected to be dubbed Fountain Alley Building.

“New York has tons of rooftop bars and restaurants, but they only have good weather maybe three months of the year,” Hayden said. “We have the potential for sunshine 365 days a year. Our rooftop bar will take advantage of the great weather here.”

The office building will be six stories high and is expected to total at least 50,000 square feet. The project also will have ground-floor retail such as a restaurant.

Gary Dillabough, who has teamed up with co-working startup WeWork to revive and renovate the adjacent and historic Bank of Italy office tower, is planning groundfloor retail for that highrise.

Those two efforts, along with more retail and possible restaurant uses in Fountain Alley that connects First and Second streets, have the potential to create a lively strip of merchants that stretches south from East Santa Clara Street.

“We will have a great restaurant, and find ways to really activate the ground floor of our project,” Hayden said. “It will be a place where people will want to congregate and gather and really be part of that community.”

Urban Catalyst anticipates breaking ground in 2021, timing that coincides with the expiration of an existing tenant’s lease, according to Hayden.

The lounge on the rooftop will be more than 5,000 square feet in size and patrons will be able to reach it through a dedicated elevator.

“We believe that the rooftop bar will have beautiful views,” Hayden said.