Usually it's a 3x3 area with an extra space for the door opening thing. If you walk diagonally from the right edge of your tree, the third diagonal spot will be the right side of the tents, and then walk two steps more to the left and those 3 blocks will be the top of the tent, walk down two more blocks and you'll have your 3x3. I hope that's clear enough to understand.
If you have chip or nat though it's a lot more though. Just search Redd's tent or Katrina's tent in Google image search and you should see what it'll look like, or just wait until they actually show up and you'll see where to place to tiles and the next time your tiles won't be destroyed.
It'll probably be easier if you just don't worry about it and let the tiles be destroyed. Unless your patterns are really specific or something, it'll still look like a gap in the path no matter what you do.