Whether you choose between a plastic rooftop cargo box or a metal rooftop carrier depends on your view of three things: weather, security and speed.
Your stuff won’t get wet if you use a plastic roof box. A metal rack can’t give you that peace of mind unless you use a waterproof cover.
A plastic box keeps things out of sight. And when something’s out of sight, it’s out of mind.
A plastic box doesn’t require you to tie down your goods. You chuck it in, close the lid and lock.
A metal roof rack pales in all those areas. But a metal roof rack lets you transport stuff quicker.
Swing your things onto the roof, strap down and slip away.