: . . . I need a workbench. Nothing fancy...
: I'm not doing cabinetry, so it doesn't need to be perfectly flat
: and true. If it holds my stuff and gives me a reasonably clear
: space to work, I'll be happy. . .

: I'm debating about what to use for a surface, though. I figure a
: single layer of 3/4" MDF will suffice for the bottom
: shelf... it'll just be used for storage.

You might look at melamine covered particleboard for that bottom shelf, too. The plastic (melamine) coating is easy to keep clean. Spills from most fluids wipe up easily. Price may even be less than MDF. Support your shelf every 24 to 30 inches if you think you'll store power tools there. They can get heavy when you have a few, and putting in support now will prevent the shelf from sagging.

: The top workspace: I'm
: tempted to lay down two layers of 3/4" MDF, then a single
: layer of 5mm "utility hardwood plywood", as Lowe's
: calls it.

Fast and study tops are made from 2x8s, 2x10s and 2x12s. You get the 1 1/2" thick top you are thinking of, but you only need to cut them to length. Without the workbench being completed you'll have a juggling act trying to cut sheets of plywood to size with just your 2 sawhorses for supports. If you go with plywood see if you can get your dealer to cut the 4x8 sheets down to whatever size you need. You may pay a dollar or two for this service, but if there is a panel saw in the store, take advantage of it.

How deep is the top going to be? It appears to be about 24 inches or more. Assuming it IS 24"---> That would mean 1 or 2 2x10s and a 2x8. Combined those give a width of 26.5", which would cover the 24 inch frame and give an overlap of 2.5 inches. You need the overlap so you have something to clamp to. These boards do not need to be joined to each other, but you can glue them if you want to. Put the 2x10s on the outside and the 2x8 in the middle. You could use 2x4s or 2x6s, but I'd go with fewer boards.

My father's workbench and mine (which he built for me) are covered with a disposable piece of 1/4" tempered hardboard (it used to be called Masonite) I think I saw him replace that only once in 40 years. It did get an occasional coat of paint--usually from drips from projects, so the color varied from end to end. I recommend it over plywood. The relatively thin veneer face of plywood gets chewed up with shallow cuts and will turn to splinters in a year or two.

Take a look at metal "bench dogs" in hardware catalos, like Rockler's. These fit into holes you drill in the top of the workench. Tap them in and they serve like clamps. Buy 2 to 4 of them first, then drill the holes for them. Try it on scrap 2x4 before committing to drilling in your workbench.

: I'm tempted to put that big vice of my Dad's in the
: front left corner of the workspace, so I'll probably build up a
: 2x4 support under that corner to support it. That vice is heavy,
: and I don't want it moving.

: Any thoughts?

First: the word in this case is "VISE". If your dad had any vices, I don't need to hear about them. You might want to change the spelling of the title on that picture you have, too, before it gets you a XXX rating.

Second: there are three mounting holes on the vise. If you are working with a base of 2x10s, you can center those mounting holes on the board and have a strong mounting. Make sure you don't drill too close to the support frame of the workbench. You need to put a washer and nut on each mounting bolt. Leave enough room for the washer, and you should have enough room to get a wrench on the nut.

If you use two sheets of plywood you'll need to glue them together to get better stiffness. It still won't be as stiff as the solid wood 2x stock, but it will be pretty close. After you have applied an even layer of glue, clamping the plywood together is pretty hard, so use screws spaced about a foot apart. Start roughly in the center and work out from there in roughly a checkerboard fashion. Drive them in and after the glue has set, pull them out. You don't want a lot of buried screws if you can help it. You might end up drilling into one when you install the bench dog holes. Even if you get the plywood cut to size you'll still do more work to assemble the top than if you use dimensional lumber.

When you attach the final layer, be it thin ply or hardboard, use very few screws and put them in back corners. and spots you won't generally be working on. Nothing dulls a plane as fast as hitting a screwhead. If you use any glue to hold this top sheet in place, use it sparingly so you won't have a lot to sand off when it comes time to change the top.

Good luck with your project.

PGJ