I get a lot of questions about where we start our seeds.
Two years ago I had my husband nail up a shelf in our unfinished basement, and we hung a fluorescent light above it. This worked, but I wanted more space.
Last year we enclosed a little "seed propagation room" in the basement. The space is under the stairs above, so it's out of the way. We insulated and sheetrocked the walls. The floor is bare concrete, we were going to put some insulation foam/pad thing down, but decided it wasn't too cold. I just put a floor mat down and it is just fine.
We put in a little 4 shelf indoor/outdoor greenhouse in the room and a radiant heat panel. My husband wired the outlet for the heat panel to a thermostat, and it comes on and goes off according to temperature. I up the temp in the morning (to between 70 and 75) and drop it at night (between 60 and 65).
Instead of the traditional fluorescent grow lights, we had read a bit about using LED lights and decided to try them out. They are really something. They really work (and they make the room look so pretty!). The combination of red and blue LED's make a full spectrum light source. The lights are on a regular wall timer and set to come on at 6 am and go off at 9 pm.
Then we figured out that there still wasn't space for all the dahlias, and now there is a large greenhouse outside for the dahlias...
And next year, we will probably decide that it isn't big enough, and need to upgrade again... :)