Raised garden

[eman]

I'm in the planning stages for a spring garden.
Looking at doing a cinder block bed 3 blocks high 30 blocks long and 12 blocks wide.
Has anyone done this type of garden? i was thinking of putting down plastic before laying the blocks and filling the bed to keep the weeds out? Or should i just roundup the area first?
Am going to plant my veggies in the main bed and herbs in the holes in the blocks. i read somewhere to plant marigolds in the holes as they are a natural insect repellent Anyone heard of this?