If you think about the ROI return on investment for a garage home office it really makes sense. The additional cost to add a 10x22 home office is a fraction of building a room addition attached to your home with the same square footage.
We looked at adding a second floor which would keep the garage footprint smaller but they were concerned that as they aged the stairs could be a problem. They considered putting their garage office in the back of the garage. The problem for them was it brought the garage too close to their home. The best option was to add the garage office to the side of their just like the garage in these pictures.
They decided on a 34' wide garage which is the widest garage we could put on their St Paul lot. In St Paul the side yard setback for a gargae is 3' so a 34' garage with a 3' side yard set back on each side fills out the 40'.