The idiomatic expression "to build from scratch" means to start with nothing and create something new, usually by assembling or constructing it piece by piece. Full definition
For example... since I have always had an affinity for computers, several years ago I used to build them from scratch for clients. (littletechgirl.com)
It's likely that editing will be more practical than building from scratch in many instances. (washingtonpost.com)
Many of the featured houses are designed and built from scratch by the owners. (remonline.com)