Looking to add multiple classes (beyond the basic 3 total) to my pathfinder character sheet.

Generally speaking I'm going to be making a character that has 6 classes, not for an efficiency thing but because it sounds fun to play this character idea. However I can't seem to find a relevant post about adding more slots of 'classes' I want to add another 3 classes to this column of line items, any way to do that with roll20? Or should I use a secondary pathfinder site that does this particular use-case better? I'm unsure where to head in this case, hence why I came here to ask the professionals :-) Any help is appreciated!

If they aren't casters, you might be able to use the same line for any class that has the same hit dice.  Keep track of the individual classes in a notes section or on the Bio & Info tab.   To be honest, you could probably put all melee classes together on one row if you wanted.  Just roll your hit points outside the sheet and add them manually.  Total up your bab, saves, etc.  Put the lowest skill ranks per level in the calculator, and all other ranks not covered by that in the misc. field.

I had thought of that before, my issue is hitdice, and skills. I can make do without the spellcasting as I only need 2 spellcaster classes. So I could have all D8 or D10 hd, however I have 2 hd 8 D8 (2+int) skills D10 (4+int) skills D8 (4+int) skills D8 (2+int) skills D10 (4+int) skills D10 (6+int) skills So functionally I need 3 different D10 to account for 2, 4, 6 for the skills. I also need D8 to account for 2 and 4 for the skills. So it's Ranger 2, Samurai 8, Magus 2, Warpriest 2, Gunslinger 1, Monk 3.

Hit dice don't really matter to the sheet.  They do nothing mechanically on the sheet other than roll hit points from the button.  My point was that you can roll the hit points manually outside the sheet and add them manually to your current and max hit points, so the hit dice listing really doesn't matter. For your skills, your lowest "skill rank per level" melee class gets 4 (I think), so you put that in the "per level" slot.  If I am correct, that covers monk, samurai, and gunslinger.  That shorts your ranger of 2 ranks per level.  So your 2 levels of ranger would equal out to 4 skill ranks added to misc.  Pretty simple really.