You'd pay more in fabrication costs to kludge it together than you would for cheap Uba Tuba from a whole slab. Most of the cost in granite IS the fabrication, not the stone itself. Even if they were free, it would still be around $30-$40 a square foot for labor. If you already had the tools and the skills, then it might be DIYable. But, granite is too hard and too difficult to work for 99% of even experienced DIYers.

You can always buy one and try it. If they are not solid granite (if they have a wooden back) they are too thin to use without a plywood substrate.

It takes a "diamond" blade and a high-speed saw ... and then some expensive polishing powder, and the appropriate dust control and protection. Granite dust is silica and nasty to breathe.

You are looking at specialized tools and heavy labor ... maybe several hundred dollars because the blades are not only expensive but short-lived ...

Okay -- I measured again, yesterday. I would need to cut them down to size, but the sides that would be exposed would be against the walls anyway. It would just be a matter of cutting, not finishing any edges. The tables are 60" x 30" and 48 x 48.

Now, is there any problem with using a plywood substrate? It sounds like it would be similar in theory to plastic laminate, but a darned sight better. The granite is about 1" thick, maybe 7/8" thick. I have a wrought iron cart I bought in Italy. It has granite that is about the same thickness. The granite pieces are sitting within an iron frame, supported by some iron cross-bars.

Merely cutting it would be so expensive and complicated that someone would probably not be willing to come out and just do that on sawhorses in the yard, then?

Frankly, if you could find a backyard granite fabricator, I wouldn't want them in my home. Only the guys who used to work in shops and maybe have had issues with drugs or jail will be the ones that don't have a "home" in a shop. Reputable fabricators wouldn't touch the project.

For DIY, it will involve purchasing a lot of tools and a steep learning curve. If you're handy, and want to approach it as a hobby project to spend your time, that's one thing. But to save money, nope. It will cost you money to do this, not save it. Pretty much any metro area will sell you 5-6 basic granites for around $40 a square foot installed with none of the hassle of trying to wrestle things yourself or dealing with the criminal element in your home.

When we needed some black granite for our fireplace hearth, we found a prefab 3x8 slab for $10 a square foot so one can find a nice solid black 2 cm granite for a very low price.

Prefab slab means that it came cut to a certain size and with a simple laminated edge profile on at least one long edge. Most of them are 2 foot wide for a standard counter and they just need to be cut to length and get any edge treatment needed on any exposed sides.

Like others here, I don't know if the granite tops on those tables is an appropriate thickness or just a thin layer mounted on plywood. You might find a plain black piece of granite about as cheap and you would know that it is a solid usable piece of granite.

For our fireplace surround and hearth, we hired a fabricator to make the surround from our kitchen counter remnants and the hearth from the black prefab piece we found. That job was cutting 4 rectangles, polishing the exposed cut edges (no lamination, just a simple eased edge) and installation. We were charged around $500 for the fabrication and installation.