Along wide face of side rails, mark at 22mm, 600mm, 1160mm, 1720mm and 2298mm and square a line across rail. Use combination square with rule 25mm from body to mark 2 screw positions at each line. Drill countersunk holes at screw positions.
With cross rails on edge, butt them into side rails centred to marks on side rails. Using drill and 4mm bit, drill through countersunk holes into cross rails. Using 100mm stainless-steel batten screws, screw through side rails into cross rails.
On 2 adjacent faces at 1 end of 1 leg, mark for a rebate 40mm deep and 85mm long. To cut rebate, set saw to cut 40mm deep and make multiple passes with saw. Use hammer to knock out waste timber and smooth rebate with sharp chisel. Repeat for other 3 legs.
Spread glue on 1 corner of rebate and place 1 leg on end so it sits over rails in corner. Clamp this assembly. Screw through leg to rails using 75mm batten screws. Repeat to attach other 3 legs.
Set saw to 45º and cut ends of braces. Place on inside of corners, predrill and screw into rails and legs with 75mm batten screws.
Round edges of tabletop boards on ends with sander. Lay boards on table frame so they overhang 40mm all round with a 5mm gap between them. Use 5mm packers to keep gap consistent. Using screw positions on side rails as a guide, draw chalk-line to mark line of screws.
Use combination square to mark 25mm in from edge of each board along each chalked line. Countersink at these points, then screw boards to table using 50mm decking screws.
Make a rectangle by butting stool uprights into cross pieces flush with the ends and nailing together. Repeat to construct a second rectangle.
Stand rectangles and nail one cross piece to join them in the corners flush with outside of rectangles. Repeat to place cross pieces in all four corners of the rectangles to create a stool frame.
On 1 of the 408mm-high sides, screw 1 face board to frame so it extends beyond top of frame by 22mm. (Use another face board as a guide.) Continue laying boards on this side with a 5mm gap between them. Turn frame and lay boards on the top. Butt boards tight in corner where they meet. Continue laying boards on top and other 408mm side to cover 3 sides of frame, leaving bottom and 2 sides open.
Attach end boards to open sides of frame, ensuring ends are flush and align with face boards.
Repeat Steps 8–11 to make additional stools, as required.
Sand table to remove chalk. As merbau leaches tannins, let it weather for 4 weeks, clean, then apply 2 coats natural decking oil to table and stools, allowing to dry between coats.