Please define DIY misting system?
Is your definition buying components and assembling the system yourself as apposed to a commercially available kit.
Or do you intend to build your own components.
This months Reptiles had an article on Misting systems and there is more info available in that article than I can begin to write in a few lines. If Mist systems are something new to you, I suggest reading the article, if only while leaning against the rack at Barnes and Nobles.
As far as the timer, the one pictured and even with the ones Bart suggested I highly encourage a drain system for any enclosure fitted with a mist system. It can be a simple as aluminum screen glued to the end of a pvc coupler at the appropriate height in a terrarium pond. Or a screen glued to a convenient hole in a cage base, covered with larger aggregate.
There is probably more ways to do it then this thread will see posts. A good start is describing the enclosure its intended for and the species in which you will be misting.
Also keep in mind Fog, Mist and Rain can all be created from the same system with mild changes to the components.
Cheers
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Jeremy Payne
JB Reptile
1.0 Snow "Kahl"
0.2 Triple Het Moonglow "Kahl"
0.1 Orange Tail Hypo Het Leopard
0.1 Double Het "Sharp" Snow
1.0 Ghost
0.1 DH Ghost
1.1 "Kahl" Albino
1.0.2 Hypomelenistic
1.3 Pastel Hypo
0.1 Anerthrystic
0.0.2 Normal
1.1 Morelia Clastolepis