I'm trying to plug in my custom inverter cell (inv_1) into picorv32a design and run the openlane flow..the runs are OK but placement of my cell isn't legalized (attached is a section of the post-routing layout & the inverter cell highlighted is my cell)..can anybody help?

Looks like that your cell boundaries include the rails, is that correct? Does your cell height (as reported in the LEF file) match the site height?

That's something I am not able to figure out @Ahmed Ghazy.. I checked out the original inverter's .mag file..the total WIDTH x HEIGHT of the top cell (outer boundary) is 1.76 x 3.20 while the inner boundary is 1.38 x 2.72 (as shown in the attached pic)...when i do a lef write the SIZE (for original inverter) is 1.38 x 2.72......while for my custom inverter of same dimension (1.76 x 3.20) generates a SIZE of 1.76 x 3.20 while doing lef write....Im attaching both the layout and extracted lef for the standard as well as the custom inverter

You can control the "inner" boundary with

property FIXED_BBOX x_ll y_ll x_ur y_ur

. Or more conveniently, adjust the box tool in magic on the inner boundary you'd like to set and use

property FIXED_BBOX [box values]

That would be really helpful..I will try and let you know👍

Could you share the LEF file?

Sure..

The issue that the rails you've drawn aren't of the same width as the other std cells nor are the upper/top boundaries perfectly centered at the rails they overlap with. For example, you want your rails to look like the following:

Thanks for the analysis @Ahmed Ghazy..will work on it