Top on or off on my C&C guinea pig cage?

I will be getting two guinea pigs. I have researched intensely and vigorously about these cute little piggies. But there's just one thing I don't know. Top on or top off? I will be ordering a C&C cage kit online. I like how the cage looks with the top off. But there's one problem. My cat. During the day, while I go to school, my cat is left at the house. My cage will be up high, on top of my bookshelves or my table, but I'm still a worrier. I close my door to my room every day as she is a small cat, she's never gotten a door open. I'll even to go as far as to spray lemon juice on my door to repel my cat (it works on the garbage can). But I'm still worried. I hate the look with the top on, it makes me think of a laboratory. What should I do? They may be perfectly fine, but I still worry. Help please! It would be greatly appreciated!