First you get need one piece of Toyota Rav4, preferably in a van version. This depends upon your local tax regime but in Denmark it is highly recommended as car tax in this case is only 50%; otherwise it would be 180%. The only draw back of a van version is that it only seats two adults and one small child.
The next thing you need is a lot of hours to construct the antenna platform including mast and the interior design. You may choose to do like I did and engage professionals or embark on a major mechanical design and interior decoration tour yourself.
The final touch is a dash of APRS.
Below pictures are from the first dry-run.
The hospital is over 100 m high. So quite a nice mast I have, huh?
Monaco, JN33RR, September 2009.
Hanstholm, JO47HC, July 2010.
Bo, OZ2M, www.rudius.net/oz2m