His fame rests on an early modernist/Futurist theoretical architecture project called La Città Nuova (The New City) carried out around 1914. This was essentially a series of speculative architectural sketches and renderings that astonished architects of a modernist bent over the years as well as the architecture-appreciating general public, myself included.
A fairly brief Wikipedia entry on him is here. This Italian language site has both a brief biography and a link to a timeline.
It's out of print, but so far as I know, this book by Esther da Costa Meyer is the most comprehensive work in English dealing with Sant'Elia. She mentions that the Città Nuova concepts were largely un-buildable as depicted.
Regardless, Sant'Elia's renderings make for very nice art in themselves, regardless of their architectural merits.
A design for an architectural competition. The rendering is by Sant'Elia. According to da Costa Meyer, the extent of Paternoster's participation is unknown.