Have a look at these different freewheel pullers. Which one appears to match the freewheel that is installed on your wheel. If you have difficulty with this, it might be a good idea to send a clear picture of your freewheel so that we can help.
Or, just take the wheel to a local bike shop and ask them to remove the freewheel for you. Ask also, what puller they used and order that one, perhaps even through your local shop. That way you will be bang on sure that you are getting the correct freewheel remover.
There is also a good chance that the shop will not even charge you to remove the freewheel. Even if they do, it would be a good idea to strike up a relationship with the shop. Doing so might prove helpful for other little problems that may crop up during your build.