Alister Turn Our Sheet? And Should I go up a size when layering?

I bought two alister turnout sheets at the Dover tent sale this weekend. They are 600D and cost $55. I can return it and was wondering if I should. Does anyone know anything about this brand? Or know if a good brand that isnt expensive. Also, I am going to be layering. I have no clue how to other then buy a no fill turn out and put coolers under it. Should I go up a size? Please help!! Thanks!