critique/paint over wanted

[gerbenpasjes]

Very thorough job with perspective grid, but as said above shading can be impoved. I think problem here might be with not the best reference choice. On your ref light is coming from everywhere and there is almost no sign of shadow. You could find another ref for form painting preferably with strong direct light, maybe like here https://imgur.com/a/pfJnoVZ

In contrary to what the people above have said I think the perspective is also wrong. Yes, the shading needs some love but before you can shade a cube, you first need to draw the cube. 




Also note that the picture is taken with a long lens; that means there is hardly any perspective distortion. This is not wrong, just be aware of it. It helps to draw the floor as a grid in perspective, so your mind's eye can form a picture of the space. Without the floor that becomes a lot harder. 

Keep it going, hope that helps. Work those grids!