Starting your own garden seeds indoors is a great way to get the plants you really want, avoiding the standard and often monotonous seedlings found in big box stores. Once your seeds are up, though, you need to ‘bump up’ into larger containers to make them grow big and strong prior to planting time. This gives you a head start on the garden. This is especially important in hot climates, as you want the plants to set fruit before the heat sets in.
This is where a cold frame comes in. Cold frames allow you to acclimate plants to the sun and protect your plants from hard freezes. While you can purchase cold frame kits, making your own is not that hard if you have simple carpentry skills.
Using an old window is a head start, as they work great for the lid. Leaving in the glass in is appropriate for cold climates, but in warmer climates glass gets the inside just plain too hot. This is where winter weight floating row covers are perfect. You will also need to have a drop light inside to keep plants warm on cold nights.
Here is an example of one way to build your own cold frame.