I agree with PamsTiersofJoy – However, if I were doing this cake, I would use an extractor to produce even logs. An extractor is a great gadget that cake designers use to produce logs, create hair on gumpaste people, grass, etc. You can google it to see what it looks like. I finally broke down and purchased one – it is worth the investment – especially if you buy it at Michaels with a 50% off coupon.
As you push out the logs, twist them (as shown in the pictures) and place them on your cake. The good thing about these logs is that they will cover any imperfection you may have underneath. You could try skipping the fondant on the cake and simply place the logs onto a thin layer of layer of royal icing to ensure that logs will stay put. Putting fondant on the cake and adding more fondant logs on top – might make the cake too heavy.
Good luck and please, post the picture when you are done!