for whom did he build it?
For use by the Fenian Brotherhood.
Fenian Ram
Fenian Ram is a submarine designed by John Philip Holland for use by the Fenian Brotherhood, the American counterpart to the Irish Republican Brotherhood, against the British. 
who started rogers locomotive and machine works? Thomas Rogers, Morris Ketchum and Jasper Grosvenor. when? 1832 where was this company started? 1856 does the company still exist? No do you know when it closed down? 1920s why did it close down? Stiff competition and an inability to increase its own capacity. did another company take over or merge with them? ALCO purchased it but sold off later, now the building is home of Paterson Museum. where is the museum located? Paterson, in Passaic County, New Jersey. what items are kept in here? Fenian Ram, archive of Holland's life and work, etc. is there any memorabilia of the trains kept? Yes the first item that you mentioned that is kept in the museum, what is it? Submarine
wiki:13474550
Fenian Ram [SEP] Introduction
Fenian Ram is a submarine designed by John Philip Holland for use by the Fenian Brotherhood, the American counterpart to the Irish Republican Brotherhood, against the British. The "Ram"'s construction and launching in 1881 by the Delamater Iron Company in New York was funded by the Fenians' Skirmishing Fund. Officially Holland Boat No. II, the role of the Fenians in its funding led the New York Sun newspaper to name the vessel the "Fenian Ram".