Then cut out 5 pieces for the sides and the bottom. In this instance, I cut:
a 380 x 130 mm piece for the bottom
2 450 x 380 mm pieces for the front and back
2 450 x 130 mm pieces for the two sides.
(This left plenty of overlap as the finished bag was 400 mm high, by 350 mm wide and 100 mm deep)
Then sew together your pieces, sew the inside side of the material (so when you look at the patterned surface, the seams are on the inside). Sew all of the sides onto the bottom first checking that the edges will be nice and straight. Then you can sew each edge. I sewed by hand, but you can machine-sew this (I just don't have a machine that works very well)