People live in many different types of homes. Some people live in homes high in the sky. Others live in homes on the ground.

Tall buildings can contain lots of homes that are built on top of each other. This book is about building a skyscraper with many floors.

Mishelle and Catherine are sisters. Mishelle has nearly finished high school. Catherine is in her final year of primary school.

The sisters live with their parents and grandmother, in a tall building in Nairobi. They love to live high above the city, like birds in the tallest tree.

The family lives in an apartment on the 22nd floor of Tower Building. They use an elevator (or lift) to get to their home.

Catherine counts floors as they travel up and down. She wants to be a pilot one day. Mishelle wants to be an engineer and build skyscrapers.

Catherine asks, "Is our building the tallest building in Africa?"

Mishelle replies, "No, this building is about 126 meters tall. The tallest building in Africa is just over 393 meters. The tallest building in the world is nearly 830 meters!"

"Wow! How do such tall buildings stay standing?" wonders Catherine.

"Basically, all skyscrapers are made the same way. The two main building materials are steel and concrete.

A skyscraper is built floor by floor, starting with a steel frame, and adding concrete around the frame. Those materials combined are extremely strong and last a long time," answers Mishelle.

To build a skyscraper, the construction workers must first dig a very deep pit for the building's foundation.

In the same way that a tall tree has big, deep roots, a skyscraper must have a strong foundation on a layer of rock. Sometimes the rock is deep in the soil.

Next, workers make a frame for the building. They build the frame with long pieces of steel.

A framework of steel makes it possible to build a tall building. Steel can carry a lot of weight.

A steel framework is the core of the building, like a person's skeleton.

Steel can also be flexible. That means that a building can sway a little (although this is difficult to see).

If there are extreme winds, or an earthquake, the internal steel structure lets a building sway slightly.

Steel forms a core of flexible strength.

The other main building material is concrete. Concrete is a mix of materials like sand, cement, and water. Workers mix concrete to make a thick liquid, which they pour into frames around the steel structure.

When concrete sets, it becomes solid, like rock. This makes the building's floors and walls.

Workers build a skyscraper upwards, floor by floor. Lower floors must support a lot of weight. Concrete can support that pressure, making the building strong and stable.

The concrete is a layer around the steel framework, protecting the metal from water and air. (Water and air cause metal to rust.)

The shafts for the lifts are also built during this stage. When the steel and concrete structure is complete, workers install windows. Then they add ceilings and walls and complete the floors.

The building needs electrical wiring and a network of pipes for water and sanitation.

Finally, workers put in lights, doors, cupboards, and other things for living and working in a skyscraper.

Mishelle says, "Many big cities are running out of space. Tall buildings make good use of space. When I'm an engineer, I'll help to build the tallest skyscraper on earth!"