I began shopping for a large construction loan to build a new car wash on the land. 

HighLevel - plenty of build outs for LOs or brokers.

I've seen estimates of $200 to $400 per square foot for SoCal with $700 sq ft for something higher end and building up a hill and but possibly higher for San Francisco Bay Area (lhigher labor costs, etc.).  

Instead of platforms like Angi, try building relationships directly with contractors, architects, and developers.

But my experience over the last 10 years of building new homes is that NOTHING comes down might stay the same but will rise almost annually Like Cement always goes up in Jan. 

I appreciate your energy and readiness to learn.

Quote from @Kaushik Sarkar: Hi,I am looking to invest first time with a turnkey developer,  who is buying the land and building a multi unit commercial retail center and some apartments.

He spent 20 years building it.

Staying on the same page and building trust.

Glad you are setting aside money, but if the HVAC is 20 years old, or the septic system has never been pumped, or the roof is 25 years old, etc; you will get hit with a cost before your build up enough set aside.How stable is the other tenant?