I was able to reverse-engineer a system of spell-building that works for about 90% of the spells in BECMI. What I learned was:
1) Some spells are simply too powerful for their level. Among these are Sleep and Fireball. It is no coincidence that these tend to be the most beloved spells of casters everywhere.
2) Different types of spells have very different trade-offs for range and duration. It is apparently much easier to create a long-duration enchantment than a long-duration blast, for instance.
3) It is possible to use the system to assess which spells are more or less powerful for their type and for their level, but it is hard to assess whether spells of different types and levels are scaled correctly against each other. E.g. we can say that Hold Monsters is more powerful than Hold Person and so should be higher level, but we can't assess whether Hold Monster is better than Fireball because they are of two different types. The types are intra-type balanced.

The system can be found in ACKS Player's Companion. It's open under the OGL for those who wish to make use of it elsewhere.

Quote from: rawma;911762In D&D 5e, Transmute Rock (added in Princes of the Apocalypse appendix or the Elemental Evil Player's Companion) can be cast on a ceiling, and causes 4d8 damage to creatures beneath it (DEX save for half), which is not very impressive for a 5th level spell; its main use is to make the ground four times slower to walk across. In OD&D the spell simply mired creatures that could not fly or levitate (sinking if heavy enough or losing 90% of movement otherwise), with no mention of damaging any target directly. It seems unlikely to me that the spell could affect rock deep enough to fill the space beneath it unless the ceiling were very, very low.

I have encountered other more or less abusive uses of spells, like polymorphing a whale into a mouse and then dispelling it at an opportune moment to squish every opponent in a small dungeon room, or casting an unattached wall of stone horizontally above an enemy force so that it would fall on them. Lots of spells were rigged to undercut potential unbalance (cannot attack and remain invisible, for example.) 5e has mostly preempted most such ideas. But I think there needs to be freedom for the DM to adjudicate an unexpected use that is particularly effective in a given situation, like dropping the muddy ceiling on fire elementals, which might be more vulnerable to such damage.

Thanks. Sounds like the GM had decided the spell would tend to result in complete cave-ins, which he figured would be game over for almost anything.

Quote from: amacris;912006I was able to reverse-engineer a system of spell-building that works for about 90% of the spells in BECMI. What I learned was:
1) Some spells are simply too powerful for their level. Among these are Sleep and Fireball. It is no coincidence that these tend to be the most beloved spells of casters everywhere.
2) Different types of spells have very different trade-offs for range and duration. It is apparently much easier to create a long-duration enchantment than a long-duration blast, for instance.
3) It is possible to use the system to assess which spells are more or less powerful for their type and for their level, but it is hard to assess whether spells of different types and levels are scaled correctly against each other. E.g. we can say that Hold Monsters is more powerful than Hold Person and so should be higher level, but we can't assess whether Hold Monster is better than Fireball because they are of two different types. The types are intra-type balanced.

The system can be found in ACKS Player's Companion. It's open under the OGL for those who wish to make use of it elsewhere.

That's very interesting.  I recently tried to do something similar, and I think I had some good ideas on how to approach the issue, but I ultimately realized that it would still be a ton of work compared to value it would bring me.  I wanted to have my own system where you could create a new spell, and it would be relatively straight-forward to assign it a level.  In the end, I just decided to reduce the spell levels from 9 to 5 (as I mentioned above), and give some very abstract guidelines for what makes a level 2 spell versus a level 3.

As for your third point, that it's hard to compare different kinds of spells...I think that this is true to an extent, but I think you can actually compare Sleep and Fireball, since they are both offensive spells.  They way I look at it would be to ask three questions for an offensive spell:

1. How many creatures can be affected?
2. What's the total number of hit dice it will take out, on average?
3. What the maximum hit die total for a creature that will usually be taken out by this spell?

On the other hand, comparing Create Food and Water to Fireball could be a bit daunting.  When it comes to spells like these, you have to determine the relative value of that category of magic and decide, as someone mentioned earlier, what types of things that magic does better than others in your setting.