The Swastika will be quiet easy I think.
Look on the Net for either an Ura or Omote Manji image, many images available, this will give you an idea for the dimensions.
Ura and Omote Manji are the same symbol in mirror image to represent different sides of the same thing(think Yin/Yang).
The Germans tipped the Swastika onto the tip(rotated it 45 degrees),
hence the Hackenkreuz is NOT a true Swastika.
Best way to do the flag i would say would be with blank coloured decal sheet(your LHS should stock a selection of those):
Red Decal rectangular for Flag
White Decal circle
Swastiak cut from black Decal
Funnily enough no bad image was associated with the Swastika till WW II, prior to that it was an often used image(US Boy Scouts, etc).
It is originally thought to be an ancient buddhist symbol, but can be found in many cultures.