This instructable will be focused on insetting this particular object, but you could do pretty much any shape in the same way.
What you'll need for this:
1 big board for the table top, good wood:22.5 x 17 x 1 3/8
4 legs: 1 3/4 square, however high you want it, in this case 29 inches
4 hangar bolts
4 threaded inserts
1 Fro mini greenhouse
1 thin flat, straight piece of scrap wood
some scrap MDF and/or plywood
Tools you need:
Router, 5/8ths bit
Drill and related accoutrements (variety of bit sizes)
Sander and sandpaper
Circular saw and/or mitre saw
Woodworking tools for chiseling the corners
Step 1: Make your measurements
Next, mark out the places you are going to rout. Here I'm making a space for the greenhouse and two inset coaster type areas The greenhouse, miraculously, was square, so we could just trace its footprint where we wanted it (1 inch from the sides and the back). The coasters we also traced from a can of rubber glue or something. The coasters are approximately the size of the largest possible cup or bottle anyone would want to use.
Step 2: Mill out the rectangular area
All this is illustrated in the pictures below.
After routing the rectangle, chisel out the corners with some woodworking tools. I actually used some chisels meant for linoleum printing. They work just fine.
Step 3: Making the coasters
To make a large circle you have to first figure out the right size for the circle. You want the radius of the full circle to be the radius of the coaster plus the distance from the edge of your router base to the outer cutting edge of your routing bit, as illustrated in the diagram below.
Once you've figured out the right radius for the guide circle, attach the thin, flat piece of wood to the router and nail it down at the appropriate radius. Cut the circle out of your material of choice, in this case plywood. Practice routing the coaster on some scrap wood before you move on to the real thing.
Step 4: Attaching the legs
Next you want to drive the hangar bolts into the legs. First mark the center of the legs, then drill a hole. You want to drill a hole the appropriate size for the bolt, but you don't want to stress the wood too much, so you should widen the hole in stages. We used three stages. To drill the bolt into the leg, you stick a nut on one side and then use a socket attachment for your drill.
When you screw the leg into the table top, they will straighten out, even if the inserts and/or the bolts aren't straight.
Step 5: Finish it up!
Since it's rather tall, I am thinking of installing a grow light panel underneath and put some plants down there. We shall see. For the moment, there it is.