Chasuble
This is a semicircle of material with a radius from the neck to between waist and mid-thigh. Hem it into a cone-shape and cut a hole big enough for the head as near to the point of the cone as convenient.
The garment is worn straight over the head like a poncho ('casula' means 'little tent'). The neck hole should be cut as a square, and the seam should be in the middle of either the front or the back of the chasuble. The seam should be covered with an orphery (a band of material going from neck-hem to base-hem in a different colour, suitably embroidered), with another opposite. The neck hole should likewise be hemmed in a contrasting colour and decorated, and the base may likewise be hemmed.
Alternatively, the chasuble can be made as a wide tabard reaching to just above the knee at the front (just above the dalmatic), and slightly longer at the back, and a quarter to a third of the way down the arm with rounded edges at the base. It has no side seams, and should have a simple circular neck opening.
The chasuble should be made from a suitably expensive material (dyed wool, silk or linen) and may be lined in plain or coloured silk or linen. The chasuble is only worn by the celebrant at Mass, making it a particularly important vestment - it should be embroidered in suitably expensive fashion!