S8 doesn't pay more for basements or even garages.You may want to check into that before wasting money on upgrades.Regarding what to do, do NOT do anything until you find an investment path that will exceed your current ROI.

Also they have a great team to work with to help customize your ad campaign(s).

I have been talking to a contractor about entering into a partnership to build a new 3000 sq. ft. custom home on my lot. 

If the firm has good technology and software to communicate with customers there's a high probability you'll get a quick responses on a regular basis.  

Making the potential customer work to see if he is interested is a sure fire way to make him say “I’m not interested.”You put out a lot of puffery, but no facts whatsoever to let people know up front what that puffery is bottomed on.

After several years of this method, a spot check of total balance due from my schedules differed quite a bit from the mortgage lenders’ balance due.

Hello, I just wanted to check on the possibility of this.

I am currently a Sales rep that drives long hours during the day from customer to customer.

Quote from @Maxwell Banton: It's math.You currently lose $12,000 a year.You spend $30,000 to customize the home and bring in more bookings.You gain $12,000 in bookings, which means you are still $30,000 behind.Next year you gain another $20,000 in bookings.

A somewhat easier process to just buying raw land and having to develop it and build the house, would be to find a subdivision where a builder is actively marketing and building either on spec or building for customers like yourself.