For installing Gnome desktop environment in FreeBSD 10, the following steps can be used.
Install the needed packages
pkg install gnome-desktop gdm xorg xf86-video-fbdev
Add the following lines in /etc/rc.conf
gnome_enable="YES" moused_enable="YES" dbus_enable="YES" hald_enable="YES"
Reboot the machine. It will boot into Gnome login screen.
Free and Open Source Software Knowledge Base 
I am getting a timeout error while installing gdm . The error is as follows :
pkg:http://pkg.FreeBSD.org/FreeBSD:10:amd64/latest/All/gnome-icon-theme-3.12.01.txz: Oeration timed out
Similar error while installing Mate :
pkg:http://pkg.FreeBSD.org/FreeBSD:10:amd64/latest/All/webkit-gtk2-2.4.9.txz :Operation timed out