How heaps yard of textile will I inevitability to variety a scarf valance for a sliding square door which measures 104"? The scarf valance should not come scallop too much so that persons...

The scarf valance should not come scallop too much so that persons can enter and exit the door minus hitting it - so I figure no more than 10" per scallop.
Which curtain colour will be best suited for...
Answers:    If I read between the lines your question correctly, your curtain rod is 104" long above the door and you are looking for a scalloped valance which does not budge past the rod (i.e. to touch the ground on both sides).

104" is only shy of 3 yards and you call for some extra for the scalloping. I would start with 5 yard of fabric and trim it final if it was too much. 5 yard is a safe number though and I construe 4 yards would not be ample on a rod of that length.

Good luck!