It's beginning to feel like spring ...

It's early March and it's time to get the greenhouse in order so that I can start the seedlings for an early spring planting. This greenhouse is old (20+years), all glass, small (10'x12') and leaks like a sieve which is why I stapled plastic all around it. I need at least one more year out of it. I've planted onions today; Walla Walla and another type called Ailsa Craig. Supposedly their both sweet onions and very large. The Ailsa Craig is suppose to grow to be around 5 lbs each. That's one big onion. I can't wait to see them. Next up to be planted are my flowers (for cut flowers) broccoli, cabbage, tomatoes, eggplants etc.. Lots of fun. I think I need a bigger greenhouse. Actually this morning I went to visit a fellow who had an 18,000 sq foot greenhouse for tomatoes. He quit 2 years ago (so why am I thinking of buying one? ... who knows) I'm actually thinking of buying part of his structure so that I can build a 36'x24' greenhouse. Anyone out there have any advice?" Do I go used to save money or do I buy new? Do you actually save money or does it end up costing more than buying something new and state-of-art? Any advice would be appreciated.