House Rules for 5e

[Sadras]

You only get the 5x Con Modifier once.

Fighter with 20 Con
1st level - 1d10 + 5hp
5th level - 5d10 + 10 hp
10th level - 10d10 + 15hp
15th level - 15d10 + 20hp
20th level - 20d10 + 25hp

Levels it out some this way.

May I ask what your motivation for this is. Constitution has already taken a back seat in Skills and Saves why would you want to gimp that Attribute further. I'm just curious.
In our group we base hit points predominantly on size, so we stop rolling for hit points at 6th level and only gain 1 hit point thereafter, so our Con Mod only works till level 6.

We use this model
Diminutive - max HD 1/2
Tiny - max HD 1
Small - max HD 3
Medium - max HD 6
Large - max HD 10
Huge - max HD 15
...etc

With your houserule you just seem to want to gimp Constitution and I'm not seeing why that would be the case.

I do like your armour class base starting at 8 though, nice touch.

 

[ardisian]

With Constitution adding to HP, even in a slightly more limited manner, and adding to natural healing - adding con modifier to each HD spent for healing, I do not see constitution being a weak stat. If it does end up being weaker than expected then I may look at allowing the con modifier to add to death saves. Right now Constitution feels too powerful, at 20th level potentially adding +100hp to your characters total HP. Base Fighter HP w/o Constitution at 20th level (taking averages) would be around 124hp. Allowing Constitution to almost double what you get from your class feels way too powerful.

 

[Pallidore]

I like your AC Proficiencies Table. It will throw off, a bit, WotC's calculations (about opponents, etc.) for levels past 4, as many characters' AC, on average, will be higher than at present. Given that a great deal of the susceptibility to easy gakking is in the early levels, it will be late to the party to help that problem, of course.