Er...you know the prefix says mobile? Mobile doesn't have granite or marble...and also, there's wooden platforms at the side of the tower so I can shoot down at the enemys. Since you haven't replied yet, I've decided to upgrade it a bit. here's the picture.Its definitely not good, but its also not bad. Something I would recommend is the use of block combinations and when to use platforms.
In this situation, the wood platforms don't match up with the grey brick. Try replacing them with grey brick or some other block that will match up, like maybe marble.
Finally, the explanation of block combos. Grey brick is a good block to intersect with wood, but in some cases it makes the build look dull. If you`re going for a cooler and more fancier watchtower, make a smooth marble base and a smooth granite triangle on top for the roof, and use the same idea you used for the top views, but with marble. The top view on this will go something like
3x Smooth Marble Across
2x Smooth Granite Up, hammer the last top block to a half block
Sorry this was really long, send me your results.