Playing as an OoS wizard and, in an attempt to get the spell scroll rules laying flat, I consolidated most of the rules from the DMG and XGtE for making, using, and copying spell scrolls. I left a few things out (like the spell scroll table based on rarity) that added to the ambiguity, and hopefully clarified a few things regarding the process and requirements. I tried to keep it 95% RAW/RAI with some Homebrew only to make it clear. Let me know if I missed anything. Open to suggestions on making it better. 

A spell scroll bears the words of a single spell, written in a mystical cipher. If the spell is on your class’s spell list, you can read the scroll and cast its spell without providing any somatic or material components. Otherwise, the scroll is unintelligible. Casting the spell by reading the scroll requires the spell’s normal casting time. Once the spell is cast, the words on the scroll fade, and it crumbles to dust. If the casting is interrupted, the scroll is not lost.

If the spell is on your class’s spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully. The DC equals 10 + the spell’s level. On a failed check, the spell disappears from the scroll with no other effect.

Once the spell is cast, the words on the scroll fade, and the scroll itself crumbles to dust.

If the scribed spell is a cantrip, the version on the scroll works as if the caster were 1st level. Casting the scroll uses the scroll user’s stats and concentration, if required. Unlike material components needed for casting, components required for the spell’s effect must be available per the spell for the casting. 

With time and patience, a spellcaster can transfer a spell to a scroll, creating a spell scroll.

Scribing a spell scroll takes an amount of time and money related to the level of the spell the character wants to scribe, as shown in the Spell Scroll Costs table. In addition, the character must have proficiency in the Arcana skill and must provide any consumable or cost descriptive material components required for the casting of the spell. Moreover, the character must have the spell prepared, or it must be among the character’s known spells, for the time spent in work in order to scribe a scroll of that spell. The scroll level is determined by the creator, who expends the single spell slot at the completion of the scroll on the final day. If consumed during spell casting, the material component is consumed at this time. 

Spell Scroll Costs

*one day equates to 8 hours of work. A workweek is 5 days. This time can be broken up and divided amongst players who meet the requirements for creating spell scrolls, as long as they work together. 

 A wizard spell on a spell scroll can be copied just as spells in spellbooks can be copied. To determine if the spell can be copied from a spell scroll, the copier must succeed on an Intelligence (Arcana) check with a DC equal to 10 + the spell’s level. If the check succeeds, the spell can then be successfully copied as normal using gold and time. During the copying process, the scroll can still be used as normal, but is destroyed and cannot be subsequently copied. Once copied, used, or if the check fails the spell scroll is destroyed.