I have a 6 by ten tent type GH.
6 foot is nice, lets me have bench/table on each side and a path down the middle.
If I were to build a small one, I would only build a lean to on the south side of a solid building. Roof, south wall and one end out of clear sheeting. Other end would be with walk door. And every thing would be solid enough to stand 60 MPH winds.

Ours is 16 x 10 all glass with an aluminum frame. It was perhaps not the cheapest but the way it is built it easily stands up to our Zone 4-5 snow and we anticipate having it for a long time.

Budgeting is important, on the other hand, spending more up front will usually pay off more in the long run. I spent more than I should have for mine, but I also have a 20 year warranty on it. There's a 5 year warranty on the heating and cooling systems, and they were reletively inexpensive, so won't be hard to replace when the time comes. I also got mine from a greenhouse company that has been in business here in Texas for many years, so I feel comfortable that they will be around if/when I want to make modifications.

Speaking of modifications, even though my GH is glass and powder-coated aluminum frame, it is expandible should I decide to make it larger at some point. I can also upgrade the heating and cooling systems, or add misting or drip irrigation. I love the fact that I have options and I have been happy as a bug in a rug with it. Another thing I can do is to exchange the glass panels for the polycarbonate ones and all parts are replaceable if anything breaks. Every part of it is labeled with a code number that identifies when it was made and where it went. Cheryl