وَبَنَيْنَا (constructed): A building is something which is connected without any cracks.
سَبْعًا شِدَادًا (strong heavens): Refers to the skies. Till now, no one has been able to know exactly what the skies are. However, the scholars say that the sky is everything which is above you, some others said that the sky refers to stars, moon and everything else. But this fact remains inaccurate till man one day discovers its essence through science.