His work is defined by bold line work and washes rather than heavy oil painting. Giani preferred the immediacy of tempera and watercolour for his interior schemes. He drew inspiration from the ruins of Pompeii and the Raphael Rooms in the Vatican. His compositions often feature Roman motifs and mythological figures set within architectural borders that create a sense of three-dimensional space on flat walls.

Modern collectors value Giani for his energetic sketches and preparatory drawings. These works capture the initial spark of an idea with a freshness that feels contemporary. His use of sepia tones and ink washes fits well in modern interiors. His prints offer a connection to the grand scale of Italian palazzo design through a smaller, more intimate medium.