Dear Busayo,
Since legal requirements and other specifics of setting up an NGO are often governed by the laws of a specific country, we are unable to provide any specific advice for you there. We can give you some ideas about where you might find some information.
Chapters 8 through 12 of the Community Tool Box have information about developing a strategic plan for an NGO and structuring the organization. You might find them helpful.
Another suggestion is that you might contact local NGO's to ask if their leadership will provide you with some guidance and advice. They will understand the local requirements, and be there in person to perhaps provide additional assistance and advice.
I am sorry I cannot be more specific and I hope this is helpful.
The Community Tool Box Advisor