Even some of the more experienced people on here said that the project you're describing would be out of their element.

This hands-on approach enables me to obtain useful information, allowing me to make informed judgments and alter my investment strategy as needed.Analyzing these precise elements of a property gives me vital information about its potential.

we build affordable units by doing higher density and I can sell or deliver a housing unit at a lower cost by sharing common elements like slabs, hallways, centrally designed systems, etc 

What has worked for me over the years is to tell everyone I interact with that I buy houses and what type of house I'm looking for.

Your post is confusing because an HOA cannot make a modification to a common element and then charge 1 owner for that *UNLESS* that owner or their tenants damaged the property to begin with.

Again, the BiggerPockets store has some books for this or you can learn by watching podcasts, reading blogs, and interacting on the forum.

There are a number of guidelines the IRS has for performing a proper cost segregation study (which will pass in the event of an audit) Here is the link to that list on the IRS website:Cost Segregation Audit Technique Guide - Chapter 4 - Principal Elements of a Quality Cost Segregation Study and ReportI have never seen a DIY before, but I'm sure people do it.Depending on the size and type of your property the fee for engaging a qualified engineer-based firm to conduct the study can be as low as $3,000 (lower in certain cases), and the significant benefit created well outweighs the minimal costs.

Are they considered Common Elements and/or Limited Common elements. 

Again, the BiggerPockets store has some books for this or you can learn by watching podcasts, reading blogs, and interacting on the forum.

What I see (from their website and from reading and interacting with them on BP) is the following1.