The best way to place barricades are in the diamond position due to the player still being able to travel through but zombies can not.
This pattern looks like so: (Apologies for the dots, the formatting messed up when just using spaces)
...............X
...........X......X
.......X..............X
....X....................X
.......X..............X
............X......X
................X
Buy the barricades while on sale and fill the inside of your little base with turrets. I would strongly suggest that you do not do this solo, join random games or set up a session, as the other players will take some of the aggro away from you. Of course this involves luck due to you will need the other players to know what they are doing for to make this easier.