Take a look at my profile, I am in the midst of designing a UDemy style course to help with getting started.  

@Marcus Auerbach - Most urban and suburban cities/towns require someone to assume responsibility and also take liability for areas of design and construction which affect public life, welfare and safety.    

But if you are going to take this as a step in a direction that you think you want to make a career out of designing functional spaces  and know how to make structural decisions and how that effects design, then I would suggest looking into architecture as a career.

A lot of the time the design firms have a couple of designs that they have had success with and recycling them.

The legislature shallprovide for the determination of true cash value of such property; the proportion of truecash value at which such property shall be uniformly assessed, which shall not, afterJanuary 1, 1966 exceed 50 percent; and for a system of equalization of designated realand tangible personal property in lieu of general ad valorem taxation.

I own a construction company and I am also an architect with years of design-build experience as well as real estate investment and development on a small scale. 

@Eric Teran may be along shortly to discuss the benefits/value of design and you really couldn't go wrong picking up a book called "The Modular Home"  by Andrew Gianino.

Would you mind sharing how did you find the contractors for this project, who did you use in terms of design/choice of materials, etc.?

Cost is the same for each size tile and the 12 inch tile definitely looks better than the 16 inch in terms of design (although they are both technically the 'same' style of tile).

I am a professional Architect.Apart from regular building design, I designed many big and small scale commercial and residential renovation projects, However this was my first hands on(literally, looked around for the cheapest and good material and hand carried them to the site.) flip as a Real Estate Entrepreneur, where investors put their money and I put my sweat equity in terms of design, construction drawings, permit and construction management.It was a Gut open rehab.