Ideally for West Africa, China will move their production eventually to them, through heavily unfavorable deals and low wages. However this will help the population get trained and (economically) on their feet to start their own companies. The only problem for most countries in West Africa is that they have weak governments. While China has a despotic, unfavorable to human rights government, it is also very protective and tends to be quite partial to the national companies interests. Without it, foreign companies would steal resources and cheap mass-produce without improving the country on the long run, as it happened in other regions.

China stripping all the resources at a fraction of the international price, raping the environment, hiring zero locals, and building roads and railways that go from some place useless to another place useless.

No, It's really not helping locals.

Yep, I forgot about the masses of Chinese workers currently there (e.g. Ghana). One can only hope rising Chinese standards and wages will eventually convince them to hire local instead.