I purchased the same SunGlo through Costco about 2 yrs ago. The one they sell is an 8 x 12 and I purchased an addition direct from Sun Glo. At the time it was on sale and the sale price allowed me to increase the size without really costing more. Mike Lowenstein at Sun Glo is a really wonderful person.
Sunglo Greenhouses
For my application, I would say I spent just under 5 G. I changed things around.
1. Installed a natural gas line because NG is much cheaper here in Michigan than electricity and installed a vent-free NG 20,000 Btu forced air heater. I use the 240V electric heater that comes with the kit s my backup.
2. Changed the electric panel to fit my desires by splitting the breakers to add circuits.
3. Installed lighting along the roof so I can use it when the winter nights come at 5PM...The GH looks really coooool with the lights on at night!
4. Added additional wire shelving.
5. The headroom is only about 7+' at the peak and I wanted more room so I wouldn't feel "closed-in". The narrow walk area (30") is tight enough. I chose to build the GH up on a wall and insulated the walls and floor with 3.5" of styrafoam. By elevating the GH it matches the height of my deck.
All in all, I think it is a reasonable pruchase for the money. You can purchase larger from them. I would make the initial purchase through Costco... not a memeber, find another family memeber who is or a friend.... order online using their memeber numbe and have it shipped to you. Then give Mike a call and add on, if that's your desire....build bigger than you think...you won't be sorry...trust me!
A downside for me and maybe just for me is the condensation on the inside. And now I have some algae growing between the panels....
PM me if you have other questions...but from my research 2 yrs ago, this is about the most bang for the buck.