The chances that you will be able to find the perfect base will be slim to none, so when you find something suitable for the size of your group(if you have one) you will need to find materials to "up-armor" the location. Below is a lite/description of some of the most basic and available of materials.
What To Use
Lumber: Great for a quick wall, wood can be found in excess at any lumber yard/ home improvement store. Rage zombies will most likely be able to climb this if you do not take the time to "properly" place the wood. A good rule of thumb is to build a seven to eight foot high fence, this should minimize a Ghouls climbimg attempts. The wood wall may also burn down, so try and implement a dual wood and earth wall. Asides from physical barriers they may also be used for fortifications and the building of platforms or watch towers.
Plywood: basically big flat sheets of particulated wood that is compressed, a popular building material to use, they come in a wide range of thicknesses. 3/8" or thicker plywood will provide decent covering on the inside of windows and unused doors. Plywood, will degrade when in a humid/wet environment, so keep extra sheets lying around in a cool dry place for replacements after rainstorms.
Aluminum Roofing: Another easily found material. Can be used for a plethora of fortification purposes. should be intermixed with other building materials such as lumber, brick, blocks, and sandbags. reasearch into how the currogated roofing sheets are attached to other materials so as to provide the most secure method of attaching, minimizing loose ends. can be used to provide fire proofing to roofs and wooden walls.
Barbed & Razor Wire: Great addition to any fence base, and top. may also be placed around windows and unused doors to help deter/slow down forced enterance. Also and be used as "trip wire" if place around shin hight to slow aproching hordes.
Chain Link Fence: This is more of a "first line of defence" fortification, as it works better to slow things down than to stop any kind of attack. A determined raider or zombie will be able to climb it. You can attach bells to help alert the watch of an attack. Also, you can also electrify it to help deter raiders and zombies if you have the power to spare. Can be used over windows or unused doors to improve the baracade.
Brick: Can be found in most home improvement stores. Building a wall will take some time and patience with the knowledge of mixing mortor/cement. Be sure to use multiple layers and a foundation to increase the stability of the whole wall against being pushed over by hoards of zombies or raiders.
Cinder Block: Similar as brick, but easier reinforce with rebar, and lumber. Cinder blocks are also much larger, which means much quicker fortification. One row of cinder blocks does little to impede bullets, however.
Sandbag: A great idea for any base, as it can make any wall bullet-proof and are simple to make, just put sand or dirt in a canvas bag. May also be used to help fire proof structures.
Tyvek: is, to the eye, a large white expanse of something remarkably like paper. Upon closer inspection, however it proves very different: it is absolutely waterproof, it is not possible to tear it, and it crinkles much more loudly than cellophane. It comes in rolls eight feet tall and about a hundred feet long. Nearly everything about tyvek suggests a tall, strong fence that rustles loudly to warn of intruders.
Simple: Some times simple is best, such as making a small ditch out side you base to trip up some slow moving ghouls. Alowing you more time to deal with them as they come. To make this more effective add sharpend sticks or some like items to "catch" the dead to further slow them down.
Places To Protect
Windows: Placing aluminum siding on the inside, fill the center with a few sandbags or place brick/cinder blocks in the center, then cover the outside with wood planks/aluminum.
Doors: Any unused doors should be filled in the same as the windows post above. Doors that will be used should be reinforced with either aluminum or metal bars. To secure the door close, you should use an old-school wooden block/metal rod used in conjunction with quality deadbolts.
Entire Outside Wall: As best you can, you should either cover the exterior with aluminum or sandbags to keep the structure you are inhabiting as fireproof/bullet proof as possible. This should also help strengthen the structure.
