This is kind of a specific question. What would parchment be like? Would it come in sheets, or be in a big roll that you could simply tear off x number of feet and start writing?
I ask because I want to have Ginny write a letter to Harry, and she keeps starting over in the middle of it, and I was wondering if it would be ok for her to tear the top of the parchment off multiple times Rita Skeeter style and still have enough to write a fairly lengthly letter.
Considering most essays are described as "inches" instead of pages, this suggests that parchment comes in rolls. Of course, the books aren't described as giant rolls, so clearly the wizarding world has pages.
I say it's up to you.