Exactly what Version of RPG Maker is being used for this Project.As a few pointers from me screwing up with my old Account,try to add some more information before Starting a Project,get a good base standing which you have a pretty good piece of,and also until anyone knows which version of RM your using we can't seem to help.But here is help for all.
RM2k-This will be a Hard task with the Crapiness of this Version of RM,with good classic tiles it still wouldn't fit maybe try RM2k3 or XP/VX
RM2k3-Same as above,but probably easier in the long run with this Edition,I think this Project is more of an XP than anything though.
RMXP-Great Choice of RM for such a Project due to it's Good Sized Characters used in it,but also try using a ABS (Action Battle System) include actual Guns with Zombies that can die and Respawn for More Fun,add Ammunition limits for Realism effects in the Game,Add Detailed landscapes with many uses of the Various Scripting Features in the Program.Sorry if thats Over the Top but with RMXP,this could be a wicked awesome game
RMVX-Might I suggest RMXP because it's possible here,but I think RMXP is more of an Action Horror type RM and VX is better with RPG's with it's nice World Layers and Tiles from the Originals.But if this is used make sure you get your Scripts strait,with RMVX many Useful scripts won't work as planned because of many Program changes in the Scripter.But also try thinking about importing bigger sprites to add a better feel to the game
Thanks for reading my Various Solutions/Comments to each version depending on what your using,and Please do not Comment on my Noobie account Status because my old account was lost
but Im back please ask if you need anything,im pretty experienced with all Versions