The hardest thing to do when you make a big size drawing, besides keeping your health always in a good shape, is maintaining your mood properly, or your drawing might not have the "mood" you want in the beginning, or you might make some mistakes you just don't wanna know. My final project is planned to be 7 drawings range from the biggest, about 2 x 1.5 m, to the smallest, about 75 x 50 cm. And you can't make a mistake in final project. Well, you may, but it has to be the kind of mistake you can fix. There is this kind of mistake you can't fix you just want to kill yourself, like a disease. Final project allows you to have a flu, headache, some back pain and all, but you just can't have HIV, or lupus, or leukimia. There has to be a "cure".
Shit happens during final project. One of my friend's work got this disease that is very difficult to be cured, you sort of need to amputate some of it part. I've made a lot of mistakes too, but luckily, I found cures.
You see, a big drawing requires constant hatching and of course, plenty of time. This is when mood comes in the way. A bad mood screws those, then your final project is probably screwed too. Then you are screwed.