For the last 4 years, we've done school mostly in our home office, which is on the second floor. It's furnished with a few bookshelves, a large L-shaped desk that Ds10 and I share, and a very comfy loveseat. Our play room is also on that level, so it's made it easy for me to keep an ear on my little ones while homeschooling Ds.
This coming year, I'll be homeschooling all three of our older boys, so I expect we'll have to spread out more. I'm not sure exactly what that will look like, but I intend to keep the office as our "home base", and still do the majority of my teaching there. We're going to move the loveseat into the master bedroom so that we can fit a small table in the office, and we'll probably make use of the desk in the boys' bedroom. Fun kindergarten stuff will probably take place in the playroom.