Yeah, Nigeria is tricky because so many scams were based out of there (still are to an extent). Really sad because legitimate business there now suffers, even just someone trying to build a pc like you.
If you need help getting parts there, I can likely assist... I'm experienced with customs and such. But I'm in the USA. To get it there properly there will be customs fees, postage fees, you know, fees for the heck of it pretty much. It's the postal systems way of making money I guess.
You'd likely pay the customs when you get the package, but I'd need to collect the shipping cost and parts cost up front. Not sure if you'd trust me to be honest and I wouldn't blame you either... But having a TPU'er of good reputation reship would probably be a sound strategy if anyone is willing. Maybe it'd be cheaper from europe, I do not know. I think to ship a "build it yourself" PC kit sans case from the United States to Nigeria would be a minimum of like $80-$100 with insurance, maybe more. But don't quote me on that... That largely depends on fitting everything in a large international flat rate box.