I'm thinking of building a llittle greenhouse

[Denninmi]

1. Have you considered one of the temporary type that fold up like tents?

Or an inexpensive kit? Both might be easier than trying to build one (but, for all I know, you could be a carpenter or builder in real life!), and might not really cost any more once you factor in materials.

Something like this:

http://www.northerntool.com/shop/tools/product_200418024_200418024?cm_mmc=Google-pla-_-Outdoors-_-Green%20Houses-_-376600&ci_sku=376600&ci_gpa=pla&ci_kw={keyword}

or this:

http://www.harborfreight.com/interests/outdoor/6-ft-x-8-ft-greenhouse-47712.html