Billboard and bus ad sizes

When trying to design our bus and billboard we came across the problem that the sizes of them are too big and we cannot create an illustrator file this big. We tried a lot of different ways but there was no way to create a file of this size. We decided to speak to Orlando and get some advice on how to  deal with this issue. He told us that the best thing to do was to half the size or divide both the length and width of the billboard/ bus ad by the same number and scale them down. When submitting them we should make it obvious and tell them that this is what we've done so that they are able to scale it up. We emailed the team at YCN to make sure that this was acceptable as we didnt want our submission to be invalid and they were okay with this.