We are at the completion stage of 9 units of room and parlour self-contained apartments.

CEMENT

About 2 months ago, we bought each bags of cement for ₦5,200 + ₦200 for carriage. We bought 10 bags in one go. But the price started rising from ₦5,400 (carriage inclusive) to ₦6,000 - ₦6,500 - ₦7,000 - ₦8,000 and more.

One afternoon, the client asked me to stock 80 bags of cement, so we don't have to pay more each time we had to stock 10 bags.

I made a call to know the current price. It was ₦8,800 (carriage inclusive). When I went to buy them the next morning, price changed to ₦9,700 (carriage inclusive).

Unfortunately, we had no choice. We had to buy it for that price and wait for several hours at that cement depot for them to supply us.

As they spent the whole day supplying those who came before us.

TILES

When I bought the first and second sets of tiles, they were sold for ₦3,200 per carton.

Just about a month later, I went to stock more and the price has risen to ₦5,400.

FURNITURE

We bought plywoods and other materials for the kitchen cabinets and Waldrops.

The total costs of materials we bought that day was about ₦2m+

72 hours later, we needed more plywoods and they were ₦1,000 costlier.

It costs more than ₦500,000 to construct a mini gutters slab

Just a few iron rods, woods, nails, bags of cement, granite, sand, etc.

Even with all these, we added some of our old materials.

CONCLUSION

I took my time to explain all these so you can have a mental picture of how difficult it is to have a budget or an estimate for a building in today's Nigeria.

Let's assume we want to focus on 6 units of 2 bedroom flat son 3 floors (the ground floor, first floor and second floor). 2 units per floor.

Considering how expensive building materials presently are, and factoring inflation into our estimate, I will have to provide this budget in a wide range to be on the safe and realistic side.

A solid foundation will costs approximately 5–10 million naira.
Decking each floor will cost 7–10 million each. Remember we have the first and second floors to deck.
We will need solid pillars to hold the structure together. Let's budget 10 million or more for that.
More than a year ago, a friend used 4 million naira to roof his 4 bedroom flat (excluding the cost of woods). So let's budget 9–15 million for roofing.
We will need 2,200 — 2,500 blocks per units of 2 bedroom flat. So, 6 units will consume about 15,000 blocks. Assume a quality block costs ₦500, 15,000 blocks = ₦7,500,000.
Labour (bricklayers, plumbers, electricians, tilers, etc.) From start to finish will cost about 8.5 - 11 million naira.
I didn't mention costs of land and documentation because they vary largely to location of interest.
Put all this together, what you will get is the costs of the skeleton. Finishing can costs so much more depending on the standard you want for your property.

Do you want ordinary locally made materials, luxury imported ones?

Depending on the materials you choose, finishing can cost 95 - 300 million naira.

Finally, as earlier explained, no one can give a sure estimate. However, the one presented here is a fail-proof one.