Twice as big as it is now which isn't bad to start with.
More storage for fabrics, thread and other notions
more wall space for a design wall as well as where I hang my quilts and wall hangings on display,
a BIG cutting table,
bigger area ironing surface,
a serger, (as well as my sewing machine and longarm which is already there),
a TV,
better lighting,
and room for several other sewing machines so I could teach classes.
A person can dream ;)