Extrude with normal is driving me crazy

Hello everyone ! I’m new to this community, and hope you guys could help me with this little annoying thing.

So I have this building, and I’m trying to extrude along the edge to make a kind of border. So I used “E” then “S” to scale the border but can’t get a good result. I guess it’s becauses the origin point isn’t in the exact middle of the mesh, but instead on the center of the original square.

Even 3DS MAX can’t get it right, but at least let me having an almost equally border in a split seconds.

So I messed around with the extrude tool but can’t get a border that has the same width on each side…
Is there a simple way to get a nice little border with the same exact width on every side without having to mess around with scale, origin point or anything ? That really bother me having trouble with such a basic feature.

Thanks !

Ensure yo have applied any object scale with Ctrl+A
Use I for inset. Hold the Ctrl key to set the depth and set the thickness to zero

Worked like a charm.

Thanks a lot !