well, let's break it down and see what comes out of it... shall we???

Gigabyte X399 Aorus MB		$359.99 --(newegg)
Threadripper 1950X		$959.99 --(newegg)
6 x 1080ti MSI Gaming x		$4799.99 --(newegg)
16GB Ram		$159.99 --(newegg)
1200W + 850W PSU		$240.00 --(newegg)
Kingston 120GB SSD		$35.00 --(newegg)
TT Flow 240 water cooler (CPU)		$137.49 --(superbiiz)
Veddha 6-9 gpu Open Case		$59.95 --(ebay)
TOTAL		$6752.40

Now keep in mind this is with all brand new parts.
Start replacing some stuff with refurbs, ditching the 1950x and getting the 1900x and I can see this dropping to ~5k.
Add to that your buddy's assembly fee (let's say $500.00) and you get a very decent 6 gpu 1080 ti rig. All fun and games...

Here comes the not so funny part of getting your money back.
whattomine.com currently estimates that rig at $9.78 /day profit... that seems a bit low in all fairness... so I'll bump that up for you to let's say $15 /day

At $6752.40 that's a ROI of 450 days
At $6000.00 that's 400 days
At $5500.00 it's 1 year

Also, keep in mind that if your buddy is charging you to host it, that generous $15/day profit will take a $3-$4 hit

Bottom line is... do you like gambling???
You could very well come on top much sooner, markets could rebound, coins could start shooting through the roof again and your ROI could be 3-4 mos.
Or you can always hold the coins and who knows... 10 years from now you could be a millionaire.

I just wanted to put some of it in perspective for you

Good luck with whatever you decide.