I don't know (much) shit either, but I believe it's very important where the greenhouse is situated in respect to north,south, east & west. IE; Morning & Evening sun, cold fronts from north-northwest, etc. Placement of existing shade tress needs to be considered. If I had to chose, as much morning sun & southern exposure. Also, covering the floor with pea-gravel will absorb heat in the day, keeping the Babies warm-er at night. A plastic Kiddie Pool filled with water also absorbs heat, to help on cool nights. The floor needs a way to drain excess water off.
Check out businesses that deal with used building material, like windows, doors, (screen or solid core doors). Used doors makes great table tops. Buying "seconds' from a cider block Co. will be great for making raised beds. Find the dump spot for the Towns mulch pile, that will be a great base. Molasses speeds the bio-breakdown in the mulch. If you use no chems. or Poultry manure, a lb. of worms in the soil will build your soil. Hope this helped. Good luck.