Building a small greenhouse with plastic sheet?

http://www.canadiantire.ca/AST/browse/3/HouseHome/PaintStains/PaintingToolsAccessories/PRD~0494804P/Plastic%252BDrop%252BSheet.jsp?locale=en <-- I have already asked a couple questions about this, and just need to know 2 more things. I know plastic wrap will work, but this is plastic sheet, and is much better,stronger and will still let light in correct? And for a greenhouse, does there need to be a few holes in the walls and roof to let air through, or should it be basically sealed completely? Thanks for any help!