This bench is easy to make because it does not require any welding.Model seen in the picture uses truss head bolts but it can (In fact I reccomend) also use flat head bolts, if counter sink holes are made into wooden details. Metal details are made of RUUKKI 25x25 retangular tube with wall thickness of 2 mm. tube is made of S355J2H steel.

It uses 2 different sizes of bolts. M5x50 (9 pieces) and M5x75 (6 pieces). With all bolts, washers, nuts, wooden pices and metal pieces together, the bench consits of 55 details, so it should not be very difficult to assemble it.