First clone the coreboot using the below commands:

----------
git clone http://review.coreboot.org/p/coreboot
cd coreboot
git submodule update --init --checkout
----------

Before you can build coreboot, it is advised that you
build the toolchain. Use the command below for that.
----------
make crossgcc
----------

Then do the menuconfig, the Linux way:
----------
make menuconfig
----------

In the options, for payload select the ELF binary option
and in the text field of binary name enter "filo.elf"
Choose 512KB has the size of the coreboot.

Wait we are not ready to build coreboot yet. We would need
to build FILO first. Clone FILO as mentioned below:
----------
cd payloads
git clone http://review.coreboot.org/p/filo
cd filo
make menuconfig
----------

In the menuconfig, deselect the Grub interface and deselect the
autoboot. Select "Include Multiboot Header". Enable PCI and FAT
support. Now do:
----------
make
----------

When you run make, it will first configure the libpayload. Choose
all the defaults except, enable SERIAL Port and choose 0x2f8 as the
address (by default 0x3f8 is choosen).
When the build completes copy build/filo.elf in coreboot base directory.
----------
cp build/filo.elf ../../
----------

Switch to coreboot directory base:
----------
cd ../../
----------

Now issue make in coreboot:
----------
make
----------

If all goes fine, you will have coreboot.rom which can be used as guest.

.:: HAPPY HACKING ::.

Sources:
[1] http://www.coreboot.org/Build_HOWTO
