How many plants are you wanting to veg ,What height you wanting to get them too.
I made mine from MDF,and just made sure that I pollyed the inside with the black and white stuff,Cut it to size then did the edges in Gaffer tape,Did the bottom 3 ft in the diamond silver refective sheeting ,it's lasted 8 year ,and still going strong.You can make the veg unit to fit the space you have perfect if you do your own.
I have a Bud Box,that I have been vegging then flowering in ,I think it's about mtr X mtr x 6 ft that would give you room to veg a few plants but I say 4 max,think that cost about 45 quid.I have a big tent that ain't even been out of the box yet 2 mtr X 2 mtr X 8 ft ,I'm wanting to use this soon with 4 600 HPS lights in ,giving them 1 mtr each to grow .But give me my own made unit any day ,the plants love it.