When they started.
duh, no shit.
Welcome to the ICMAG forums.
Have you grown anything before, vegetable garden, Cannabis?
Hydroponic has a bit of a learning curve involved, much more so than say an organic style garden with its relative simplicity of essentially just adding water, kinda.
What size area are you planning on using?
Do you want to grow traditional photo-period plants or autoflower style plants? Recreational or Medical grow, relative to genetic selection you may want to make.
Are you in North America? (Product recommendation reasons)
The "ICMAG'S OFFICIAL ~DIY~ LINK-O-RAMA" has a lot of diy ideas.
I would encourage you to use the search function here, it can quickly become your best friend information retrieval wise, if you let it.