Here is a free resource provided by Magdalena Ganestam. You can learn to draw the Cosmatesque geometric patterns. To learn more about these classes, go to her website, magdalenaganestam.com, or to her Instagram page, @magdalenaganestam. Magdalena was born in Warsaw, Poland and at the age of 12 moved to England. She now lives in Rome and is basing her designs on those she sees around her on the floors of churches and basilicas in her home city. Magdalena studied sacred geometry as the main focus of her M.A. at what used to be the Prince's, now the King's Foundation School of Traditional Arts in London.

I encourage people to take a look at this. It is a rare chance to learn this art rigorously at no cost. Magdalena hopes to develop a following and start charging for tutorials and classes for advanced study. I would like to see her able to do this. 

Cosmati decoration is an Italian tradition of opus sectile - cut work - in which pieces of colored marble are cut to shape and pieced together. It is similar to but distinct from, mosaics, which use many even-sized coloured pieces of glass or ceramic called tesserae to construct images and patterns. Cosmati is named for the family which, over three generations in Rome, established the tradition in the 14th century, and the vast majority of these designs are in Rome and the surrounding area. You can read more Cosmatesque decoration here.

Below: the design work in process.