Need Help Coding a Custom Chest GUI

I am making a mod and I have coded a very simple GUI to appear when I open a chest. Now I need help adding slots to the gui. If you could help me that would be great.

My coding for the chest looks like this

public boolean onBlockActivated(World p_149727_1_, int p_149727_2_, int p_149727_3_, int p_149727_4_, EntityPlayer p_149727_5_, int p_149727_6_, float p_149727_7_, float p_149727_8_, float p_149727_9_)
{
if (p_149727_1_.isRemote)
{
return true;
}
else
{
IInventory iinventory = this.func_149951_m(p_149727_1_, p_149727_2_, p_149727_3_, p_149727_4_);

if (iinventory != null)
{
Minecraft.getMinecraft().displayGuiScreen(new GuiChest());
}

return true;
}



My coding for the gui looks like this
public class GuiChest extends GuiScreen{

int guiWidth = 182;
int guiHeight = 187;

@Override
public void drawScreen(int x, int y, float ticks) {
int guiX = (width - guiWidth) / 2;
int guiY = (height - guiHeight) / 2;
GL11.glColor4f(1, 1, 1, 1);
drawDefaultBackground();
mc.renderEngine.bindTexture(new ResourceLocation(RefStrings.MODID, "textures/gui/chestGui.png"));
drawTexturedModalRect(guiX, guiY, 35, 39, guiWidth, guiHeight);
fontRendererObj.drawString("Grass Chest", guiX + 40, guiY + 5, 0x601959);
super.drawScreen(x, y, ticks);
}
protected void keyTyped(char c, int key) {
switch(key){
case Keyboard.KEY_E:
mc.displayGuiScreen(null);
super.keyTyped(c, key);

}
}
}