With all do respect you need to find an antenna that will work in the frequency range of broadcast FM which is from 88MHz to 108MHz, and it will have to be tunable within that range. I don't know how much simpler I can word this for you to understand. Moving this post to Beginners Area...
Look online for dipole antenna designs, use an online calculator to find the length you need for each element and construct one out of basic hardware store stuff. Dipoles are the easiest antennas you can design and will perform great for broadcast FM.