Crowdie,
It is best that you use the Visual RF offline planning tool to get an idea of your horizontal coverage for your specific space. Also, if you have an AP105, you should configure it as a site survey AP and measure your coverage using a TX power of 12 in the space based on the output of the Visual RF tool to see your actual coverage.
The AP105s, 135s and 225 are deployed in areas with 3M ceilings; you just need to test it to see if it specifically works in your space. In spaces with multiple floors, you need to stagger the AP deployment, since that RF might been seen on floors below/above due to the downtilt pattern. In that case, make sure you do not run the APs at full power to limit floor-to-floor propagation. You also might want to not deploy in hallways so that access points can leverage room to room attenuation so that access points do not have good RF line-of-sight vs. deploying in rooms.
Again, this is general advice on what to avoid and your specific space will determine what you can do. Please see the Indoor 802.11n VRD here: http://www.arubanetworks.com/wp-content/uploads/Indoor80211n_2012-05-31.pdf for detailed instructions.