All you need to do is take the width 90mm or 70mm and times that by three giving you 270mm and 210mm. You then just cut all your timber up into those lengths and sand the cut ends to remove splinters.
If you want to know approximately how much timber you will use, just take the height you want, divide it by the thickness of the timber 35mm, times that by 3 pieces per layer. So for a one-meter high stack that will be 1000mm divided by 35mm which gives you 28.5, that times 3 is 85 and a bit pieces. 85.5 x 270mm is around 23 lineal meters of timber needed to construct the game.
Please let me know if that assists or if you have any other questions.