To pick on Danny, because he's an oldby and can take it, if your character concept is 'Swampthing', then how in the world is 'Sorc/Cleric/Geomancer/M-T.' the mechanics? Doesn't that skip most of the game before your character even is well, himself? What do you do with a character who dies before they become a Sorc/Cleric/Geomancer/M-T?
WAAAAH! I'm tellin' Mommy!
*ahem*
I was actually just discussing this elsewhere, in fact.
When I design characters, I start with a concept, which could be as simple as "dude with battle-axe" to "unusually large woman who grew up the sole child of a fisherman; outgrew being able to help her Dad; apprenticed with masons; heard The Call (becoming a Paladin)- all in a fairly misogynistic, rigid caste system that prevents commoners from carrying most weapons, which is a privilege of the upper castes."
From there, I try to figure out what kind of goals- if any- such a character would have, then what kind of mechanics exist in the game support that. Then I plot out a path.
Just like as a teen I planned my path to becoming an artist and musician.
However, the plan is not set in stone. It is fluid- it is subject to change based on events in the campaign, so the character may wind up very different than the original concept.
Just like I wound up becoming an attorney and MBA. I'm still an artist & musician, but not at a professional level.
In "Swamp Thing's" case, he was a coming into an established mid-level campaign after I retired my "Indiana Jones" character because the two players running healers left the group- leaving us with ZERO healing ability. So I wanted to design a PC with healing abilities...but with enough of a flare that I wasn't just playing Sir Healbot. So instead of playing a straight cleric, I started looking for other options, and stumbled on the aforementioned schtick.
It started with finding a way for me to keep healing ability up while still being able to do something "non-clerical", and the CompDiv feat Sacred healing fit the bill. Since that meant I'd be burning Turn Undead attempts to supply healing, I obviously needed to take Extra Healing as well. As I continued to look around at what could be fun to do, I found the Geomancer PrCl...and noticed that there were "planty" options at each level of Drift. After that, it was kind of like a game of Tetris as things fell into place. His clerical side provided the link to the plants and earth, the sorcerer side provided the "fire" and additional earthy elements. And so forth.
Then it became a matter of winnowing down the many, many mechanical options into something both conceptually coherent and playable.