Do not underestimate the upgrading path of a POI - this can get you levels as you upgrade the building - not 'fast' but its there. That is upgrade able to concrete and then reinforced concrete. Cobblestone (upgraded from Flagstone that you can make) is the base route for the early part. OH! It definitely needs to be upgradeable to at least reinforced concrete for the short term. Once you get the hang of it you'll finally 'see' how much it can take to upgrade a POI. If looking for a POI its important to see if and how and how much it will take to upgrade it. Gamers4Kicks has a bunch of POI takeovers.
For building you're own base you have to account for a lot, where you want to put it. Since its fast and easy and it'll get you into the 'upgrading' part. Since this is your first time out I'd suggest a POI. Ultimately I think its now important to get out there and see how things work or don't work for you. Well - first off theres some great advice here. Place them horizontally around the columns so you can stand on them and shoot whatever is attacking the columns. Windows are good, they are cheap to make and you can shoot through them as much as you need to. You may need to repair the ramp and barbed wire as much as you can reach it without getting down, and protect your columns. They will then walk up the ramp, fall into the barbed wire, and go back up the ramp. When the zombies try to get through the barbed wire they are slowed making for easy headshots. Then make a ramp that ends with a flat block 1 space away and 1 space down so you can jump over, and surround the ramp with barb wire on the sides and ground so you can get up without being slowed. Other than that, it's pretty easy to survive the first horde by making a small bridge, 4 high, as long as you can. The Fire Station is also good, I break out the top 2-3 stairs and make a ladder with hatch on top. They tend to beat on the weaker wooden blocks and leave the supports alone. I set up in an attic, then every few blocks on the ground floor I reinforce for support columns.