"we would like to have some more storage space and a larger workshop area would be great..."
As with a lot of things having a little more storage space is always helpful.
This particular design began trying to reconfigure the existing garage into a larger workshop (maybe a future studio apartment space) and space for cars. Before long we all realized we needed more space - a detached garage idea was born. if we moved the workshop to the new garage that freed up valuable space in the existing garage for cars, better storage etc. and the detached garage could have storage space and room for a car or boat or rv or whatever was deemed necessary.
In the end we created a "home gym" in the front of the garage with a separate workshop area in the back portion and a nice carport area on the side.
The "home gym" is really a home cross fit work out area complete with a 15' climbing rope shaft that extends up into the roof area inside. Taking the existing house basement gym and all those things plus some additional free weights, cardio machines, rowing equipment, rings, jump boxes, pull up bars etc. and moving it into the detached garage allowed more space in the existing house and provided space in the new garage for everything plus some. The garage is complete with a mini-split heat/ac system, heated tile floor and ceiling fans. The workshop area in the back third of the garage has plenty of space for a large work bench and spacious work area and some storage along with a bathroom complete with stacked washer/dryer. The future potential for the workroom to convert into a studio living space may be in the thinking somewhere later on but for now they will enjoy added storage space and larger workshop.