Well, beta.. in most centers a notepad with 12-14 sheets is provided and I have never heard of anyone exhausting it completely. I understand that you do a lot of rough work but in CAT, you will be solving hardly 10-12 QA questions (if you are among the toppers) and 2-3 LRDI sets (Again, if you are among the toppers). And for that, the notepad will be more than enough.
There are some centers, however, that do not provide a notepad. I have heard of a few that provide 1-2 A4 sheets to students. If you end up landing at a center like that, ask for extra sheets in advance. The invigilator won't mind. But ask in advance, tell him politely in the beginning itself that you do a lot of rough work. Nobody would say no.