The viola is a difficult instrument for the maker because the model has not been standardized. Hence player preferences can vary widely. The height of the ribs, length of the body, width of upper bouts and scroll style all make for a different feel and sound. To help account for these differences, I generally make two different models of viola.
The first model I make is patterned after a viola by Andrea Guarneri. This model has been called by many players the perfect viola. It is large enough to make a huge viola sound yet the narrow sloping of the upper bouts facilitates playing the upper positions. I have substituted the violin-style scroll for the cello-stlye scroll as it is easier for the player.
The other model I use for violas is patterned after an instrument by the Brothers Amati. This instrument is slightly smaller in length and rib height. It also has a violin-style scroll. It is beautifully proportioned and produces a very pleasant tone.
Either of these models can be dimensionally adjusted to suit the players needs.