[RPG] ny reason to pick an odd number for Constitution

From Special Abilities – Nonabilities:

Nonabilities

Some creatures lack certain ability scores. These creatures do not have an ability score of 0 – they lack the ability altogether. The modifier for a nonability is +0. Other effects of nonabilities are detailed below.

(emphasis mine)

So yes, they add class/type HD +0 each level.

The simplified versions of character creation are:

1. player uses a pre-generated character—either from "out there" or that you've built,

2. someone builds the player's character for him or her, or

3. player builds side-by-side with experienced person.

Your players have ruled out number 1, but I don't think there's anything disingenuous about presenting both options 2 & 3 as "player creation" options. It's just a matter of who's holding the pencil, doing all the little maths, and making decisions when the player doesn't yet have a preference.

During the last few months I've had seven or eight opportunities—some in my own campaign, some in Adventurers' League—to walk new and new-ish players through character creation. With some I've just had the discussion, absent any rulebooks, of what the possibilities are and what they might like to play. With others it's been sitting and flipping PHB pages with them, line-iteming the character sheet. In the first instance I'd estimate about a five-minute conversation followed by 10min. busywork; the second instance I find it likely to run a good half-hour. (It did on Wednesday, even with a guy who'd been playing for a few months and I was helping make his second character.)

Remember, the list of decisions to make isn't just race/class/background: it's:

1. Name (people find this one of the hardest)

2. Race, perhaps sub-race

3. Class

4. Ability score disbursement (go back and find those racial modifiers, too)

5. Choose some skill proficiencies, languages

6. Starting equipment: weapon, armor, perhaps another weapon, which pack to take, sometimes a fifth bullet-point which is mostly flavor and thus is second to "Name" in how much time it'll take

7. Archetype (Domain/Oath/School/Tradition/Circle/etc.)

8. Background—and now I've picked up different skill proficiencies and perhaps a language slot, so perhaps need to change original choices. I've also picked up different equipment, so perhaps need to change those original choices.

9. Let's fill in the weapon attack table

10. Magic: If you've got a spellcaster, "choose four from this list of twenty--they're all in the following eighty pages."

And there are many more pair-interactions than just the Background ones I explicitly pointed out!

So I'd say you should talk to these players about at what level of detail they want to be involved in character creation. If it's acceptable to have a five minute conversation with each, you spend a day filling out some character sheets, then another five-minute conversation discussing how you implemented their intent that'll speed things along a lot. You go away with notes on their interests, send them away with the basic rules pdf. Those what come back knowing all the rules—encourage them to re-tool their characters on their own time. And be ready to make small in-game tweaks to characters in recognition of the fact that it was you that wrote up the character rather than the player.