Please for the love of god, drop that idea of creating another social network, throw that idea of another “SIMPLEMACHINES” forum out of the window of the nearest high rise and watch it fall to its death 30 stories below without regret. There are some areas in Nigeria and Lagos in particular that require a much needed shot of some “source code” into its veins. These include:
1. Property leasing/letting/rental: In a city of more than 9 million people, getting a property for lease or rent in Lagos is like going through the proverbial eye of the needle. It doesn’t just make sense that in the 21st century I still have to go through some semi illiterate middle men called “Estate Agents” with their exploitative charges and fees, before I can get a property to lease or rent. I don’t see the reason why I cant do the whole process of searching, viewing and paying for a property via the web. This sector is hot and needs a startup with excellent implementation to just “nail” it.
2. News and information services: Why I cant get real time, localized news and information via the web or by sms kind of beats me. For example, why do I have to get stuck in traffic on Ikorodu road when FRSC or LASTMA can just send me alerts and advice me on alternative routes to take? Why do I also have to get stuck in between the cross fire of rampaging thugs in Fadeyi area on my way back from work, when security forces like the police can alert me and advice me to steer clear of the area? I surely would not mind paying for a service like this. 
3. Web payment gateways: This sector is a no brainer but the players in this sector are either bereft of ideas or have some sort of hidden agenda. There cant be innovation in the sector if developers are not making money from what they are doing. I do not see the reason why we can’t have our own “Nigerian Paypal” since Paypal has refused to come to Nigeria. The only very high barrier to entry of anyone interested in going into this sector is CBN’s bureaucratic bottlenecks and red tape bullshit before you can get licensed. But its hot and ripe for innovation.
. Disclosure: I am working on something in this space.