How much space does runes of magic use

It depends on how many runes are needed.
For example: For Wind Wave, you will need Air Runes and Blood Runes. If you have any type of staff of Air, you will need 1 slot. All other spells will need at least 2 spots, 1 Air/Element rune (depending on the staff) and the combat rune (Mind, Chaos, Death, and Blood). The only exception is Water spells, as a Tome of Frost can be used from dungeoneering, combined with an air staff and you will only need the combat rune.
For Ancients, You will need space for water runes, air runes, fire runes, soul runes, blood runes, death runes, and maybe chaos runes if you are level 50-72. The ancient staff is recommended or better (best is Staff of Light)
Another note would be if you only cast 1 type of spell, you only need 3-4 spaces (4 for Smoke, 3 for Shadow, Blood, and Ice).



Note you may also consider law runes to Teleport, or teletabs (teleports are recommended as you will already have runes)
Cosmic runes will be needed with normal spellbook if you plan to alch items.
Again on normal, if you plan to bind/weaken enemies you will need nature/body runes.
On Lunar or High Level Normal, you will need Astral Runes likely.
At higher levels, it is NOT recommended to use a staff of an element, excluding the Tome of Frost (As this is an off hand item)