placing object files

[G.L. Grobe]

When a project is compiling, instead of object files being placed in the top
level, what tells them where to get placed?

Also, how do I placed new libs, progs, etc... in a separate tree for built
finals so that the src and the build root dirs would be at the same level
and finals built from the src dirs would be placed in the build roots
hierarchy?

Any example projects around that do this?

Any help much appreciated.