Grad school

[Motivation]am currently working as a civil engineer in Nigeria and preparing to apply for a phD in the U.S 2026,I have been working after my undergraduate studies and I just write normal site progress report and I just discovered that apply for grad school involve a lot of writing from SOP,cover letter,cold email,statement of interest and to be honest I don't really have the writing skills.[Question]1)is it advisable to use chatGTP to generate ideas on how to write the SOP,statement of interest etc 2)how do I know my GPA equivalent in the US or should I use my university grading as reflected in my transcript.