Thanks for your feedback!
I do understand that the top and engines are the main problem. I have tried thinking about ways to attach the top with clips but i think the major problem is that the clips are the 1x2 kinds and are white, which would kinda throw off the whole color scheme and make everything more bulky than it should be. And yes, there aren't any 2x2 or 2x3 slopes that are rightside up in this set, which is why I had to use the inverted slopes. So in a sense, I didn't run out; there just weren't any in the set in the first place.
As for the engines, I also had no choice based on the pieces included in the set. The only light grey cylindrical pieces in the set are the huge ones that I used for the engines. the set doesn't come with any 1x1x1 cylinders or 2x2x1 cylinders. It does have 1x1x1 cylinders in lime green, yellow, and trans blue, but they would look retarded, so I didn't use them.
Anyways, I have already broken up the venator
because my shelf seemed empty without my shuttle. It was just a fun little experiment that I thought I would throw it out there for people to see.