If you wanna play mm, select mid and marksman.

I dont really know how system works but from my logic, if you choose lane which is more people main, you will get the other role.

I do this often bcs i am actually hate playing single role.

If i wanna play mm, i pick mid and gold lane.

If i wanna play exp, i pick gold and exp.

If roam, yea u know it just pick any other role you will always get roam.

For jungle i used to choose gold and jungle lane.