Greetings from Chicago

This is my first post here.

I have a large Elm tree in the front yard which is causing
no end of problems in the main sewer line which runs underneath
this tree.Roots and more roots.I have decided to install a 6"
cleanout in the front of the basement floor so I can get at least a
4" cutter on the sewer rodder and cut the roots back better.
I have rodded this line 3 times in the past 10 months but only with
a small cutter because the present cleanout is on the 4" stack pipe
I'm thinking a 6" clay "Y" on the pipe but what do I come up
to the floor with? 6' Iron or clay? and what goes on top flush
with the floor for the cleanout access etc...
I'm no stranger to sewer work but this is one I haven't done before.

Thanks for any suggestions or thoughts or advice or whatever.

Scott Alger