I am in ct, my house is 90 years old, my plumbing was on the opposite side of where my new bath went. With adding plumbing, repair walk way and drive way after tearing up to add sewer lines, blending the new build into the orginal roofing and siding my 103 sq ft addition with above average but not highest end finishes cost more than $650 per sqft.

Was it worth it, to us yes but we had the savings, the equity and looked to find another house in our location with the third bath and could not find one we liked as much. Was it a sound investment, our last appraisal was higher by more than we spent to add the bath so on paper we are safe but reality might not recoup the expense at such a high return. Also we added a master bath in a house that did not have one which gives a bigger ROI than just another hall bath.

I talked to GCs to get a rough idea of cost, than interviewed architects after assessing we could afford it, got plans and retained the architect to work with our chosen GC during build and than got true estimates on scope of work according to my plans, than chose the GC and signed a fixed cost contract excluding finishing and cabinet costs.

I am right around the corner from you and can tell you that a 3rd bath adds value from a marketing point of view when you put it on the market for sale. Having said that, if you don't need one, don't go to the expense if you are staying there. Your roof is another issue, a new roof in our area of S Florida adds value. It's not suppose to - but because of the insurance issues, a roof older than 20 years old is very expensive to insure. I guess the first question is - are you planning to be in your home for the long term? Then make the improvements so you can benefit from the new plumbing, electrical, HVAC etc.

BTW, your GC is right. Have an architect design the right place for your 3rd bath if you choose to go in that direction. There are even architects right here on houzz that can work remotely.

The "general route to follow", is to hire a Certified Bathroom Designer through the local NKBA. You can search online right here: http://www.nkba.org/Design/Homeowners/ProSearch.aspx
I did a quick search & found 6 CBD professionals in your immediate vicinity.
HOWEVER! Replacing the roof & windows should take precedence over adding a bathroom, (unless of course your budget allows).
May I ask why you are considering adding a 3rd bathroom?

Thank you all for all the valuable input.

To answer your questions:

1. I am planning to add a 3rd full bathroom solely because of need. I plan to use the house for a while (my kids are young). If I am understanding correctly, it would be prudent to add a 3rd bath in this case? The house is tight and I know I will get good use out of the 3rd bathroom.

2. To answer the question from @bry911, I am planning to reclaim about 250 sq.ft of covered (screened) patio space to allow for the addition of this 3rd bathroom. Ofcourse, not all 250sq.ft will be allocated to the bathroom. I presume that would mean extending the living square footage of the house? The patio is covered by the roof but does not have air conditioning.

From the looks of it, it might be multiple projects of renovating the house. This includes the following:

1. Addition of the 3rd full bathroom.

2. Relocating the water heater from the laundry room into the garage. Wife wants a sink inside the laundry room.

3. Relocating the Air Conditioner Unit from next to the pantry (5ft x 2 ft) to the garage. Wife wants a bigger pantry.

4. Remodel the 2 existing bathrooms.

5. Add a standing shower outside by the pool. Kids running inside the house from the pool makes the house messy and wet.

6. The roof needs to be replaced. Since my house does not get too much daylight, I would like to add 1 or more skylights to make the house more airy and bright.

Can anyone recommend any GC's and architects that they have personally worked with?

A 300K project like all of that, including high wind retrofitting that will be required, definitely needs to have the order of operations of projects thought about on the front end so that you don't have to go back and repeat steps. Look on the Find a Pro tab, and look for an architect who shows remodels and no all new construction.