Hi, I was hoping someone could help me. I’m making a dress with a beautiful fabric. I have the zipper which is made to be invisible. My question is, when making the pattern, besides the seam allowances how many extra centimeters are supposed to be added (on the fabric) to allow for the zipper to be sewn on? The back is one piece, so I will have to put it on the side, correct? If so, please tell me how much extra fabric has to be allowed and wether it’s on just the front side part or the back side part? Or would it be better to make the back two pieces and leave the zipper on the back? I haven’t drafted the pattern yet, I’m just hoping to hear some tips on how to do this since it’s my first dress. Thank you!