Magic Specialization

I have listed three schools of magic for magic users in my games.  This allows for  3 specializations.  Geomancer, Potionmaster and Runemaster.

What this does, in my games anyway, is to create a little more depth of character in magic users.

MU's can perform spells normally, but are limited by their magic points which are based on their Constitution.

Magic points cannot not exceed Constitution and spell level equals points cost for each spell.  So, a first level spell costs 1 point, second level costs 2 points, and so on.

As an example, Protex is a 5th lvl magic user, specializing as Runemaster (scroll writing, etc..)

His Constitution is 13 and he can only cast four 1st level,  two 2nd level and one 3rd level spell (using the table in PHB) in one day.  That gives him the ability to cast up to 11 spell points worth of spells a day.

Once he hits the ability to cast up to 13 or more in spell levels, he cannot exceed his magic points based on Constitution.  If those magic points reach zero, he will die.

Here's where specializing in a school of magic comes in.  If Protex is a Runes Master, he is able to create scrolls up to his highest capacity of spell knowledge.  In this case, he can write up to third level spells as long as he knows them.

He can create and sell scrolls as a way to make money.   He can also write out a certain number of scrolls in his non-adventuring time (as long as the player describes his activities before actual game time) and carry around a certain number of scrolls as "backup" with him on adventures.

He cannot write scrolls while adventuring.  Not enough down time or necessary quiet environment to facilitate the work.