Don't forget to use your vanishing points to construct the whole shape and not just the bottom plane! :) From what it looks like to me, you are extruding your prism from the bottom plane rather than using the vanishing points to construct the top.

Instead of criticism, here's a step by step: 1. Draw your horizon line 2. Place a vertex along the horizon to act as your vanishing point 3. Draw a line perpendicular to the horizon 4. Draw a triangle by connecting the 2 ends of the line to the vanishing point 5. Now that you have a perspective plane, you can extrude whatever you want from it In the case of 1 point perspective, you can simply extrude 2 lines from this plane horizontally in relation to the horizon. This is your front facing plane. To complete the 1 point perspective cube, simply draw another line along the plane perpendicular to the horizon. Now you have a 1 point perspective box :) In the case of 2 point perspective, simply add another vanishing point to your horizon and connect that to your perspective plane as well. This will create a diamond shape, but don't think of it like that, instead see it for what it really is, a 3D wedge shape made up of 4 triangular planes. As far as 3 point perspective goes.. I've never tried it so I can't help you out much there. Hope this information helps :)

Your boxes are a bit distorted, this is because your lines of your box aren't comming together at the same point. A box in a 3 pp has 3 vp's; 1 vp is on the left side of the box (all lines from the box that are going to the left need to come together at the same point), the second one is on the right side of the box. These 2 vp's are sitting on the HL. Now if we look down on a box then the 3rd vp should be below the box and vice versa. 

Hey Matt, your art work in your default album, it's so very good.