How much it takes to build a Garage ?

[sunnypopali]

I am new to this forum and I am doing my internship in Accounts but recently my boss asked me to find out estimate for his new garage ? How can I explain him in this world I am learning account not engineering anyways - thought I might get some views here - here is my question.

Alloted space for garage is 20ft x 15ft, I need to know the checklist required to build garage from ground level. I know fabrication stuff but what things to consider and what to avoid.... checklist will help me a lot...

Please share.