non-root build failure + correct permissions for /usr/obj?

["Pouya D. Tafti" <p%san-serriffe.org@localhost>]

Sorry if this is a trivial question.  After a long break from tracking
current, I was trying to build amd64-current on a new system (just a
custom kernel and the modules for now).  I followed the steps
described in the wiki [1] with regard to creating and chown-ing
/usr/objdir, /usr/tooldir, /usr/destdir, and /usr/releasedir (all
owned by pouya:wheel).  Next, I tried (as 'pouya'):

    $ ./build.sh -j4 -T ../tooldir -D ../destdir -R ../releasedir -O
../objdir tools kernel=TP_X201_FR_CH modules

which eventually failed with:

[begin excerpt]
    --- install-accf_httpready ---
    --- 
/usr/src/../destdir/stand/amd64/5.99.29/modules/accf_httpready/accf_httpready.kmod
---
    #   install
/usr/src/../destdir/stand/amd64/5.99.29/modules/accf_httpready/accf_httpready.kmod
    dirs=/usr/src/../destdir/stand/amd64\
/usr/src/../destdir/stand/amd64/5.99.29\
/usr/src/../destdir/stand/amd64/5.99.29/modules;  for d in $dirs; do
/usr/src/../tooldir/bin/x86_64--netbsd-install  -N /usr/src/etc -d $d;
 done
    /usr/src/../tooldir/bin/x86_64--netbsd-install  -N /usr/src/etc -d
/usr/src/../destdir/stand/amd64/5.99.29/modules/accf_httpready
    /usr/src/../tooldir/bin/x86_64--netbsd-install  -N /usr/src/etc -c
 -r -o root -g wheel -m 444  accf_httpready.kmod
/usr/src/../destdir/stand/amd64/5.99.29/modules/accf_httpready/accf_httpready.kmod
    x86_64--netbsd-install:
/usr/src/../destdir/stand/amd64/5.99.29/modules/accf_httpready/accf_httpready.kmod.inst.00567a:
chown/chgrp: Operation not permitted
    *** 
[/usr/src/../destdir/stand/amd64/5.99.29/modules/accf_httpready/accf_httpready.kmod]
Error code 1
    1 error

    nbmake: stopped in /usr/src/sys/modules/accf_httpready
[end excerpt]

I'm probably doing something wrong; but I don't know what, since IIRC
it is mentioned in the NetBSD Guide that the system can be built as
non-root.

Otherwise, what is the good practice with regard to the location and
permissions of the various target directories (obj, tools, release,
and destdir)?

Thanks in advance,
Pouya

[reference]
[1] <http://wiki.netbsd.se/How_to_build_NetBSD-current>