I can't see the point of making the tables from "timber" at least with my local prices.
Even here "in the middle of nowhere" 2-hand office tables cost pretty much next to nothing and new table legs(steel) are like 3usd per piece. Steel frames for heavy duty use are bit harder to find.
Same here, reaadymade stuff is often way cheaper than buying timber.
But for some years ago, an local contractor used to make desks for me, just welded an frame of 1"x 1" square stell tubing, and I used an old door for the top. This contractor was building houses and stuff, and doors was often used as packaging for other doors, to keep them from getting destroyed in transport, often these extra doors was good enough for this kind of use, so I had couple of desks like that.
Now I don't have room for this anymore, but those was very sturdy and good desks at the time.