Building a grill

Hi, I have a Mazda 323f, in the US it's called a protege5.  I have had to chuck my old grill, so instead of buying one i want to make one. I have a good idea of what i want it to look like but not quite sure how to take a mold.

Here is a pic of my car with no grill:

http://www.maff5000.pwp.blueyonder.co.uk/fogs1.JPG

And, here is similar to what i would like to make:

http://corksport.com/store/large/h77i/99p-exterior_misc/AUTO_EXE_Grill.html

After reading some posts, i was thinking i would try and use expanding foam sprayed in a bin bag to get the shape of the hole, from there cut the foam. Then not sure what to do as the foam would be exact size, so if i glass on top it will end up too big, if it ry and reduce the size of the foam i will most likely screw the lines up a bit, or should i glass the foam - scoop out the foam and then use the inside of the new fibreglass piece as a mold?

As you can probably tell, i have never fibreglassed before, although i have read i lot of post on this forum.

Any ideas to help me out?

thanks

i would cut 1/2 MDF sheet into strips about 2" wide then...cut up the strips into pieces that will fit in the opening the way it is supposed to...i would put about1/8 of tape on the outside of the wood pieces..line them u in the hole so the tape is againts the grill opening...use a bit of kitty hair (mix it hot) to join the pieces of wood in-situ....after thet you can build up the MDF to shape you need on the inside , remove the tape and build up the outside in the corners...sand it to the shape you need...tape off the whole thing roll on some foil and take a mold off it...and your set to go...

long process...tough piece to build..lots of angles and thin profile...

if you do it this way be sure to foil your bumper as well.. 

Gonna have to agree with REALITYCHECK and third AUSTINCUSTOMS intelligence.  Makes total sense to use what is already there, remove what you dont want, and fabricate what you do want.  This concept would allow you to keep factory mounting provisions and with no change in your final component's integrity.  No matter whether your an MDF / FiberGlass / or Plastics-Urethane finatic, if you have a will, then theres your way.

Regarding using expanding foam....  You can fit a bag in the opening (dont set it back too far so you have allowance to pull the bag straight out)(or you can construct a cardboard form) - fill the bag with the required amount of foam - let expand fully - remove the bag from the grille opening - remove bag off of the foam plug - trim the foam plug(trim to allow desired spacing between grille and bumper/valance and hood) - TEST FIT - cut the desired design(s) into or out of the foam plug as desired - cover plug completely with tape/foil - cover half of the plug laterally or to desired depth of the grille with FG/resin and let cure - remove foam if needed - TEST FIT - finish as desired - if youve made it this far, your imagination will have grown enough to make you realize how easy it is to make the mounts as well.