How thick do you roll your fondant or gumpaste when making daisies? Would using a fondant roller be okay?

You need to get it as thin as you can It should be paper thin. Use gumpaste. Nic Lodge's recipe is the best If it has to be fondant, then add some GumTex or Tylose to it to strength it.

When using gumpaste, ideally you should be able to lay it over a piece of paper and read what's on the paper through the gumpaste. It can be more difficult to use when it's this thin, but for the most life-like flowers, this is the thickness you look for. Personally, my only preference for a roller is a smooth texture (non-wood) and I usually will use a smaller roller for small pieces, large roller for large pieces. Good luck!