Personaly I would send HandyAndy a pm if you wish to go the flat pack chassis route
He has many,many satisfied customers & knows the Roadster chassis inside out
I for one would not even contemplate cutting the chassis tubes for a second time.
When I started my build, there was no flatpack option & to be honest, I soon got bored cutting up all of that steel
Build yourself a nice elevated table, tis a real pain in the butt crawling around the floor.
Here's hoping you enjoy your new build