Maybe I need to be more specific. How far down the arms should the edge of a gothic chasuble rest? At the wrists? Forearm? Where should the lower part rest on the leg? Knee? Shin? Ankle?
You can look at the models on the web sites for ideas, but this is allowed to vary greatly, according to the preferences of the priest and according to what the parish has to provide. For instance, an altar society might purchase a set of vestments for the parish, using the measurements of a priest who is 6’ 4". Their next pastor or the priest’s substitutes for his vacation may be 5’ 10". Even if he’s permanent, he may have to make do with those until it is time to replace them. That’s how wide the latitude is, and why it is that wide. With a Gothic chasuble, if he’s not tripping or knocking stuff over on the altar with the sweep of the fabric, and doesn’t look as if he’s a 18 year old in a 10 year old’s clothes, then it’s a go. With the traditional ones, it has to be small enough so that the stiffness doesn’t make the garment appear that it is the vestment that decides when to rise and when to sit.
If weather will not be an issue, some of the synthetic fibers and blends have a very nice drape, wrinkle less, and wear very well. If the priest is going to be saying Mass in hot weather, however, have the chasuble cut as short in the width as he would be comfortable with, no cowl but a plain-cut neck, and in a natural breathable fabric with a weight just heavy enough so that the vestment will not need a liner. You might ask him if he would like a chasuble in white linen or silk, suitable for weddings and funerals, so he will never be stuck dying in a polyester chasuble in August.
Some priests have very definite sentiments about the style elements of the chasubles they wear, and some literally could not care less, at least not once the rubrics are satisfied. (IOW, “I don’t care, as long as it is made according to the GIRM.”)