Here's what I found so far.

Born: 24 November 1890 in Gelsenkirchen,Westfalen,Germany
Married: 17 November 1914, Mary Bertha Domsalla.

Ellis Island Passenger List
August Rohmann, age 38, from Malke, arrived 12 March 1902. Destination was to join brother John in Hermine, Westmoreland County, PA.
Wilhelmine Rohman, age 32, from Watchalke
August Rohmann, age 12, from Wachalke
Maria Rohmann, age 9, from Wachalke
Anna Rohmann, age 7, from Wachalke
Bertha Rohmann, age 4, from Wachalke
All arrived 2 August 1902. Destination was to join husband/father in Hermine, Westmoreland County, PA.

WW-I Draft Registration Card dated 5 June 1917 for a Gust Rohman, born 24 Nov 1890 in Gelsenkirchen, Westfalen, Germany. He was married, working as a coal miner and living in Sprinfield, IL.

1920 U.S. Census for Detroit, Ward 19, Michigan
August and Mary Rohman. Immigration year for August is 1902, place of birth was Germany, working as a mechanic in auto factory.

1930 U.S. Census for Springfield, Sangamon County, Illinois
Gus J. and Mary B. Rohman. Immigration year for Gus is 1901, place of birth was Germany, working as a coal miner. Living with in-laws, Fred and Minnie Domsalla, parents of Mary B.

Any additional information would be appreciated. Don't know if Gus and Mary had any children or when/where they died.