Question

give reason if gales or high speed wind blow over houses , the roofs of the houses can be lifted and blown away.

Answer 1

Whenever there are high winds, such as in storms, thin metal roofs on ... I see no mathematical reason why one can deduce from the incompressible flow ... If the strong wind blows all day, allowing enough time for the "air to flow in .... from inside the house pushes roof to low pressure and gets blown away.

Answer 2

When high speed winds blow over the roofs, the air pressure above the roofs gets reduced. The pressure  inside the hut is higher than the pressure above the roofs of the hut. So, the pressure inside the hut  pushes the roof and they are blown away.