I would suggest this pattern for at least the undercoat: http://butterick.mccall.com/b5425-pr...hp?page_id=872
It is the one i used, and it worked just fine. Needed some changes, but nothing drastic.
When it comes to his overcoat, it gets harder. I looked online and in fabric shops, and I could not find any good pattern. If I was unlucky, or if this is just a bloody hard pattern to find I do not know, but... I used the same pattern: http://butterick.mccall.com/b5425-pr...hp?page_id=872
This means that you will either have to re-draw the collar, or (if you use the white one) make sure that the buttons are more to the side. Here is a good picture of Undertaker that shows how his costume looks: http://s5.tinypic.com/ezlae.jpg
Be warned, though: if you are low on money, it's not an easy costume to make. When I made it, materials for two coats alone cost me over £80.
Good luck, whatever you choose to do