onmonitor setup questions

Newbie questions I'm trying to setup my spaces in onmonitor. I'm confused if you should size the Unix disk or just do it in onmonitor. My disks are currently all setup as 2 gig slices (Raid 1+0, total of 185gig). For my rootdbs I was going to use 200meg. How do I use the rest of that 2 gig drive? I was trying to create the plogdbs in it using onmonitor, but does it manage the placement in that slice or do I use the offset to avoid the rootdbs? Thanks Gary Quiring