The analysis for build-a-spell continues. 4th level is where we see the first physical transformation and creation spells in the LBB. Also, notably at 4th level, we see a couple references to affecting 4 HD creatures, implying that there may be a "target HD" variable, at least for some categories of spells.
Polymorph Self and Polymorph Others are two variants of the same basic concept, with the difference being that the first can only target the caster and has variable duration, while the second can be involuntary (with a saving throw,) includes combat abilities of the new form, and is basically permanent. "Change form" + "any form" seems like two features. Add "combat abilities" and a duration feature to get Polymorph Others, with the duration feature being something that lessens the immense power of "permanent until dispelled"; maybe the victim gets a new save every time the new form grows or heals (in other words, changes form in a lesser way.) But Polymorph Self would be 2 Features + 1 Variable, which seems like a 3rd level spell; either it's 4th level because MU transformation spells can't be a lower level, or we should add another feature.
Remove Curse is a permanent dispel effect on an item normally immune to Dispel Magic, so that's 3 Features + 1 Variable = 4th level spell.
Wall of Fire creates damaging flame that lasts so long as the caster concentrates (3 Features.) I'm torn over whether to add the double damage against undead as a separate feature, or just the nature of flame attacks on the undead. Wall of Ice is pretty much identical, except for the base material.
Confusion is a lot more confusing than it needs to be. There's the basic effect (random confused behavior,) plus variable quantity (targets,) range, and duration. 1 Feature + 3 Variables.
Charm Monster is a Charm Person spell that affects non-people (creatures that it would normally be difficult to negotiate with.) It also potentially affects multiple targets; add variable range and we have a 4th level spell.
Growth of Plants causes nearly-instant plant growth, has permanent duration, and variable area and range. I'd want to limit the permanency to a duration feature, requiring a save every change of seasons.
Dimension Door has impossible transportation with no obstacles, certainly worth 2 Features. Distance should probably be set as another feature, but what's the fourth feature? Perhaps we can add variable capacity (extra mass carried besides the traveler.)
Wizard Eye is vision at a distance from an invisible, mobile eye. That's worth at least two features, plus we can add range and duration variables. 2 Features + 2 Variables = 4th level spell.
Massmorph is actually more like a highly-specific illusion (Phantasmal Force,) without the "dispelled by contact" restriction of illusions. It also affects a large number of targets. 4 Features = 4th level spell.
Hallucinatory Terrain is a specific illusion that targets a larger area, but restricted to terrain features, plus variable range. 3 Features + 1 Variable = 4th level spell.
I'm noticing that spells are becoming harder to fit into the framework at higher levels. There are a lot of questions I'm leaving unanswered, such as the limits of things like the duration, range, or size features.