The Greyhawk Grognard has an article about runecasters.
My own solution involves 4e style rituals.
I have a rule that to cast any spell that is a ritual you need components equal in value to the spell level squared time 10 gp.
I have another rule that says that ritual take a minimum of a turn (10 minutes) to cast.
Then I created magic using classes that can only cast spell using rituals.
In order to cast spell in combat they need to create a scroll or in the case of runecaster runes.
The advantage of Runes is that you can place them in a wider variety of locations. Make a rune staff, wand, dagger, etc.
There also two types of runes. One shot runes which work just like scrolls. And permanent runes.
Permanent Runes cost double whatever you have for scrolls. But afterwards can be recharged for HALF the cost of a scroll.
determine how many rune and object can have. I ruled each rune take up a
space two inches by four inches. Basically divide the length by four
and that how many runes that can be scribed.
The advantage of
this system is that you don't have to modify AD&D's spells. A
fireball rune work just like a fireball spell. A fireball ritual works
the same as well but you would have to be in a siege, behind the battle
line, or a special combat circumstance to pull off the ten minute
I would rule that the time to activate the room is the same as the equivalent scroll.
In my campaign magic user can cast ritual equal to
1/2 the highest level spell they can cast rounded down. So when you can
cast 2nd level spells you can cast 1st level ritual. But this is optional. You can have ritual caster as a separate class and not have magic-user being able to use rituals.
effect of this on game is that the player loads up on runes to the
limit he can carry. They have more "firepower" but once expended they
have no quick way of regaining spell power. Since scroll/rune making
take days and weeks of in-game time it is an important consideration as
to when runes are used.
I flesh this out in further detail in my Majestic Wilderlands supplement.