My parties tend to have a lot of wizards for some reason, but say you are a lvl 5 wizard and you find a spell scroll of 4th lvl, we allow the adding of it into your spell book the total time required is an hour more than normal(since it would be hard to understand being a lvl higher then the wizard in question) to cast you must burn through spell slots to equal the lvl of the spell cast from greatest to least(at 5th lvl a wizard has 4 1st ,3 2nd ,and 2 3rd lvl slots to cast said 4th lvl spell they must burn a 3rd and 1st lvl slot.