Otherwise use atleast 1" hardwood board for long lasting durability imho.
0.5" plywood can hold the weight but question is for how long before it bends. There are ways to strengthen the boards by adding support beneath it and clamping the joints by metal hinges but all that will only add to the costs, so....
You will also have to varnish and epoxy paint the plyboards, so add that cost too....
Keep in mind though to weigh all the pros and cons if you're going for a permanent structure as there will be no room for error later.
So design will have to be near perfect to prevent a lot of

(damned site script, can't write h.e.a.r.t or h.a.n.d.s without making a smily out of it)
sushant wrote:Have a look at iron shelves too, I guess they should be cheaper.
