I don't hear much about places that rent rooftop tents. There may be a vendor or two that rents them to help encourage their own sales, though I have never heard of one that does.
Best bet might be to put the word out to friends and fellow adventurers, even on forums like this one, that you'd like to rent their tent for three nights.
One night in a rooftop tent will not, in my experience, give you a true sense of what it's like. I just about hated my first night in a rooftop tent. Now it is by far my favorite place to sleep and nap.
I let people climb up into my hardshell RTT and stretch out all the time to see what it's like, though I'm not too keen on removing it to let someone test it out for a few nights. Someone might, though, especially if they have theirs on a hoist and not already mounted to a roof.
I'd encourage you to explore the differences between hard shell and soft-sided fold out tents. After my own research and exploring different types, I determined the far quicker pop-up and packing back up of the hard shell tents was much more preferable than the soft-sided fold out tents. The appeal for you could be completely different.