Get Rapini's book if you want to have a quick and handy reference during sign outs. This would be best too for a 1-month rotation.
If you want a good reference text to read, get Barnhill's book - excellent for beginners. Weedon is good to buy only when you are further into your training.
I also particularly like McKee's book - I personally think it is the best Dermpath text currently out there. The clinical pictures that accompany the histology are excellent and obviate the need for you to refer to a clinical Derm text (like Bolognia or Andrews or Fitzpatrick) while reading path (which is essential if you are serious about learning Dermpath).