honestly i would never recommend DIY cause things can go very wrong unless u know wat u r doing. i reccomend those big fibreglass (blue coloured) tubs that r reasonably cheap but immune to the elements. its also extremely hardy and will last years babyyyyy woohoo
if im not mistaken u can buy it in 6' by 3' or 8' by 5' sizes....go to any credible fish shop and they shud be able to order it for u. good luck! peace....