Is root required for flashing custom rom?

[mohamed arafath]

Hi.,I had rooted my Samsung galaxy s4 gt-i9515 using odin flash tool and flashed twrp for my phone.Then,I go to supersu and i clicked the full unroot option.I check the phone with root checker that it is unroot ed or not , it says that 'the root is not properly installed'.So my question is, can I flash a custom(cyanogenmod ) rom with gapps ?, is root is required for that ?,flashing a custom rom is safe to my device or not ?

 

[B. Diddy]

Moved to the S4 Rooting forum.