There are multiple monsters that suggest they were created by wizards or humans in general. So, if I wanted to create a "mad scientist" type character that wants to create lots of monsters, are there any options for that in the rules?
I know that there are rules for creating undead and constructs, but do the rules end there?
Personal spell research.
Design a spell that has instantaneous effects, discuss with GM, implement.
discuss with GM
This part is key and cannot be stressed enough. The short answer to your question is no. There is no easy rule for you to become a monster creator. No matter what angle you take you are going to need to involve your GM, heavily.
You also need to keep in mind that your GM may simply not allow it to happen.
I once created a spell that animated small piles of wood into self-duplicating, sentient 'toothpick golems'.
I created a whole new race in the game, with the intention of having them serve as household minions in my keep.
Instead, they fled in a mass exodus and started their own community in a nearby forest, quickly building a series of traps and complex mechanical vehicles (all entirely of wood) to defend their new home from interlopers.
It was fun, but I never did get my free labor... had to wind up taking Leadership instead.
If your intention is to create a permanent creature that is both powerful and loyal (and unique), then it falls firmly into GM territory.
Honestly, I'm ok with the creatures not being "loyal", as almost every created creature also has rebelling and/or escaping in its backstory.
Look at drow fleshcrafting and especially the feat "brew fleshcrafting poison"
This seems to be more or less what you want.
I once created a spell that animated small piles of wood into self-duplicating, sentient 'toothpick golems'.
I created a whole new race in the game, with the intention of having them serve as household minions in my keep.
Instead, they fled in a mass exodus and started their own community in a nearby forest, quickly building a series of traps and complex mechanical vehicles (all entirely of wood) to defend their new home from interlopers.
It was fun, but I never did get my free labor... had to wind up taking Leadership instead.
If your intention is to create a permanent creature that is both powerful and loyal (and unique), then it falls firmly into GM territory.
So that's where Wyrwoods come from!
A vivisectionist alchemist might come close (Torturous Transformation). Alternately, the preservationist archetype with the Bottled Ooze discovery can work for instant minions. Or even combine the two (the archetypes are compatible).