roof bar

Has anyone got any recommendations for roof bars (and boxes) suitable for an eGolf? Obviously something with the smallest amount of drag and around 150 litres would be ideal. Are there any important considerations to take when using one? e.g. I'm guessing that the range estimator can't take...

Hi. I am really keen on the optima phev but have received some vague answers when asking kia about roof bars and tow bar. Does anyone have any experience on this? Been advised Cruz offer bars to fit. And tow bar should be ok. Uk spec provides no limits but EU one does....?!