Question: When you are talking to a 3rd person, fundamentally

> 
> (1) それは、**私達**の出来あげたものです。  
> 
>  (2) それは、**われわれ**の出来あげたものです。
> 
> 
> 

mean:

> 
> That is something that we all created together.
> 
> 
> 

With regard to using them as **first person, plural, possessive pronouns**, this a nuanced choice. `I'm not asking about using them as subjects, objects, topical nouns, etc. Just as possessive pronouns.`

* My feeling is that #1 is about taking more direct credit for what was accomplished? It sounds rude? Like you considered yourself the lead in a small group of 4 or 5 people?
* Even if you were the lead, always express to outsiders that *a team of equals*, among them yourself, accomplished something? That is choice #2?

Answer: 
I don't believe that there is any special difference in meaning imparted by adding の to われわれ or わたしたち・わたくしたち.

Adding の only turns these words into a possessive pronouns.

The choice between these expressions will always involve how you feel about who you are addressing and people you include as "we", regardless of whether what follows describes something you have done together or not.
Essentially, both mean "We". In my experience 我々 has the nuance of a "we" within a defined group: we (our class, our company, our country), where 私達 has no nuance. A very common use case is 我々日本人