The problem with a miter saw sitting alone on top of a bench is that you can't cut long boards: Gravity is always tipping them over the edge of the narrow metal table that is part of the saw. . You can fabricate your own fence out of a very straight piece of wood or metal or you can do as I did and acquire a commercially available moveable stop that slides along an aluminum track that features a stick-on measuring tape. Miter saws can be utilized in a workshop as a permanently affixed tool or on the jobsite as a portable or semi-portable unit. Slightly loosen the lags and nudge the table up or down with a rubber hammer before tightening the lags fully. These wood should be hand selected for straightness and jointed on one edge.
Before joining the two boards together, slotted holes should be cut into the back-up board for the purpose of mounting and adjusting the fence position on the table top with reference to the fence on the miter saw. The fence sits with its jointed edge on the saw table top while the back-up board lies flat on the table, in back of the fence, with its jointed edge joined to the base of the fence.  As for overall table height, I would suggest that you make the miter saw table so that the top of the table comes to your belt line when standing. PERMANENT SAW TABLE FOR SHOP USESince I buy lumber in lengths up to 14 feet long, I decided to make a very long miter saw table in my workshop. I suggest that the top surface be 3/4" Melamine or Formica over 3/4" particle board. This will give you a comfortable working height and still permit you to bend over the table. The miter handle must be free to move its full travel in both directions, left to right. You might want to make this shelf adjustable in micro increments so that you can get the top of the saw platform exactly level with the top of the saw table.Time and again, miter saws are utilized to make duplicate cuts of the same measurement.
My miter saw table measures 8 feet to the left of the saw blade and another 8 feet to the right of the saw blade. Mount the saw securely to the shelf using lag screws. The gap should close behind the top of the miter saw. If makeup dressing table sets you can use the entire 4-foot width of the Melamine or particle board, by all means do so, especially if your miter saw is of the “sliding compound miter” style. If you need, the space below the saw table can be left open for shelves or wood. The saw must be mounted in this gap so that the top of the miter saw table is flush with the top of the saw table. One board will be the actual fence and the other will keep it straight from behind.
A saw block must mount to something to hold it in place, usually a fence. I will take a look at the construction of miter saw tables careful to both types of installations. Cut a few equally spaced slots in the back-up board perpendicular (at right angle) to the fence

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