qgis - How to draw a square from 2 coordinates?

I have a CSV file with the following output

id, x min, y min, x max, y max, value
1 , 0    , 0    , 100  , 100  , 5
2 , 0,   , 100  , 100  , 200  , 10
3 , 100  , 100  , 200  , 200  , 15
4 , 100  , 0    , 200  , 100  , 20

I can plot the co-ordinate points onto my basemap fine. What I'm trying to do is tell QGIS that row 1 of the CSV has the bottom left and top right corners of a square, to draw it, and to assign it a value of 5.

I'm not even sure this is the right way to achieve my goal - which is to display a grid with different values attached to each square, and then produce a heat-map based on those values.

Thanks.