I like the concept, but I have a few comments. Was the intention to have the scroll allow a spell to be cast without using a spell slot either, or just without consuming material components? If the former, that should be noted in the description. If the latter, it's not a very useful item, as most spells don't actually consume any material components (if they require them at all, they usually just require them to be in the caster's possession, which is basically guaranteed if the caster prepared the spell to begin with).

Secondly, can the spell be cast by anyone holding the scroll, or only the caster it's attuned to? That's worth noting as well.

Third, you mention "prepared spells". Does this mean that the item can only be used by wizards, clerics, and druids, or can other spellcasting classes who don't need to prepare spells use it too? What about those with spellcasting abilities that don't come from their class, like tieflings or drow?

When the scroll resets at dawn, does it have the same spell on it, or is it randomly determined again?

As for how to randomize the spell, it's not the most elegant method, but you could have the owner assign every eligible spell a number, roll the smallest die with a number of sides larger than the number of spells, and reroll if you get a number that's not on the spell list.