East Side, West Side, all around town, every form of real estate, no matter the tenancy, is being sold to investors for conversion into residential condominiums. They range from four-story buildings in TriBeCa that are selling for more than $550 a developable square foot to tennis facilities in Queens to factories in Long Island City to parking garages and vacant lots.

Over the last decade, a number of office buildings in Lower Manhattan have been converted into residential towers. Last week, Kent Swig, president of Swig Equities, signed a contract to buy a 103-year-old, landmarked, 21-story, 540,000-square-foot building at 25 Broad St. It was bought in 1994 for $5 million by Crescent Heights. Crescent spent $55 million in 1997 to redevelop it into 347 apartments, 21,400 square feet of retail and commercial space, and 6,800 square feet of office space. Industry sources said the property sold for $260 million. Also last week, a joint venture of Worldwide Holdings and Lubert-Adler entered into a contract to sell an office building at 88 Greenwich St. to Thorwood Real Estate, a partnership of Joseph Sitt and Andrew Heiberger, for $195 million. The 365,000-square-foot, 72-year-old building was converted into 458 apartments in 2000.

Thorwood is also buying a building at 158 Madison Ave. and will convert it into a 22-story loft condominium.

A 95-year-old, 185,000-square-foot office building at 485 Fifth Ave. will be sold next month to a joint venture of Michael Belfonti, Adam Hochfelder, and the Carlyle Group. The partnership will pay $88 million to a group of investors including Jack Forgash, which purchased the former Rogers Peet building for $54 million earlier this year. The buyers plan to convert the property into condominiums.

Last month, Monday Properties entered into a contract to buy a 20-story, 210,000-square-foot office building at 386 Park Avenue South from Park South Control for $71 million. Industry insiders think it will be converted to condos.

The 143,000-square-foot Stuart Dean Building at 355-366 Tenth Ave. will be sold and converted into a residential tower. Insiders said Gary Barnett’s Extell Development will pay $25 million for the site. Extell recently bought the one-story Ritz Furs shop on 57th Street between Sixth and Seventh avenues, as well as the transferable air rights. It plans to demolish the building and construct a 37-story condominium tower.

New York City is losing tennis courts. Two years ago, a tennis center atop a parking garage on 31st between Fifth Avenue and Broadway was sold and converted into a Con Ed substation. The 6-acre East River Tennis Club on the waterfront at 44-02 Vernon Blvd. in Long Island City has closed to make way for a major residential development: two condominium towers with a total of 1,080 units and two rental buildings with 1,100 units.

A few years ago, Eagle Electric moved its manufacturing operations to Mexico. Earlier this year, the Andalex Group bought one of its buildings at 45-31 Court Sq., near the 48-story Citigroup tower in Long Island City. It plans to renovate the property into 238 luxury condominiums. Another facility in Astoria at 21st Street and 24th Avenue is being converted into 188 condominiums.

A 12-story, 147,000-square-foot office building with possible air rights at 63 W. 38th St. is on the market for redevelopment as residential condominiums or a hotel. A few blocks away, a 14-story office and showroom building at 215 W. 40th St. is being marketed for $22.5 mil lion as a residential conversion. A zoning variance may be required.

In May, the City Council approved a zoning plan for Williamsburg and Greenpoint. Sites there are now selling for more than $175 a developable square foot. There are two developable Gabila’s Knish Factory properties at 111-113 S. Eighth St. and 110-120 S. Eighth St. and Bedford Avenue, less than 10 blocks from the subway station at Hewes Street and Broadway. The sites are under contract for sale, and were listed for $7.5 million.

At least six other sites in Williamsburg and Greenpoint are on sale for residential conversion, with prices ranging from $100 to $225 a developable foot.

A five-story office building at 530-540 Atlantic Ave. in downtown Brooklyn is being marketed for $18.5 million as a residential conversion prospect. A 190,000-square-foot development site occupying the entire block of Myrtle Avenue between Gold and Prince streets, blocks from MetroTech and the Atlantic Terminal, is being marketed for $21 million.

A new stadium for the Mets and the Olympics is planned in Flushing. Muss Development plans a mixed-use complex on the corner of College Point Boulevard and Roosevelt Avenue on a site formerly occupied by Con Ed. It will have over 1,200 apartments, a Target, and a Home Depot. Shaya Boymelgreen is converting the former RKO Keith at 129-43 Northern Blvd. into a mixed-use facility that will have 250 condominiums, 25,000 square feet of retail, and a parking garage.

Everyone wants a piece of the real estate market. A prominent developer told me that a physician friend called him and told him he wants to join him and become a developer. The developer asked the physician if he would like him to assist him while he is performing surgery. Real estate prices have risen to records, and today is not the time for amateurs to try their luck as developers.

“I am astonished by the lack of differentiation in underwriting by the financial community when it comes to quality of sponsorship, capital structure, and location of a development,” a vice president of real estate finance at HSH-Nordbank, James Fitzgerald, said. “We remain vigilant and cautiously optimistic on select developments. It is no longer the domain for amateurs.”

Mr. Stoler is a TV broadcaster and vice president at First American Title Insurance Company. E-mail mstoler@firstam.com.