I moved up from a 4 x 6 to a 4 x 8 with a self healing reversible mat. I used a 3/4" thick piece of plywood, finished it off by sanding it, adding a trim piece that sat just barely above the edge so when I added the cutting mat it laid just inside it and wouldn't be able to move around. Added a shelf below to house all my shoebox size plastic totes filled with scraps, orphan blocks and fat quarters by color and/or size. Also have a place for my trash can and too large rulers and rotating mat. Added a couple screws to the end bookcases that the cutting table is sitting on top to hold my longer rulers but easy to grab to as I use them so much. The size mat gives me plenty of room to lay a finished quilt top onto it to trim the edges. Other times I keep a small sewing machine at one end for adding the binding using the table to hold the quilt up so no weigh pulling at the machine. I normally have each of my projects all at one end in plastic cases to keep them separate. Also have my bolt of batting above the table so when I need to cut a piece I can just pull it down, lay it over the table and cut.
Getting ready to make up an attachment to enlarge my ironing board so it will fit onto the cutting board edge for those times when I'm pressing long pieces of fabrics. This way the fabric isn't pooling down on the floor getting wrinkled again.