In my attempts to have some fun and be useful I wanted to make a few spells that revolve around nondimensional space. One of my favorite spells from 3.5 was the horde gullet, a sorcerer only spell that let you swallow things and store them in you until you throw it up (my favorite thing to do was eat marble or lap oil). There is only one though and its mainly in there as a spell to make bag of holding. I was wondering if anyone had any advice or maybe a thought process on how to make more of them.
Distance distortion was a classic.
The rules in the Player's Compendium don't really cover extradimensional spaces, so the only real guideline you're likely to find for picking the level of spells is "what problem does this spell allow the players to solve, and howdoes it compare to other methods of solving that problem?"
A bag of holding, for example, greatly simplifies the logistics of dungeon crawling and small-scale trade ventures. The spell to create a temporary one becomes available at ninth level, when players have the resources to engage in bulk trade and need to supply armies; At that point, the bag doesn't completely eliminate logistical issues, but it does simplify them, allowing players to focus on the big picture.