Building a greenhouse on a lot with fundation

I have a slightly different problem. In the past I always attached my greenhouse to the main house with a half staircase connected to which ever wall the door was on with no problem. For the first time when I tried to make the greenhouse as a separate building while the main one still had a foundation, the outer staircase works perfectly okay, but the inner one doesn't want to shrink down when placed parallel from it...
I wonder if this has always been a problem, though.
If that is the case, I hope it can somehow get fixed in the future... Would really help with smaller lots.

I have a greenhouse, and a lot with a foundation. Since you can't only have foundation on specific buildings, I made my foundation kind of short compared to usual, but I just placed the pasture grass floor tiles in the room to make it grassy and green. It still looks like a greenhouse to me, and the plants don't have to be in the planter box.

https://i.imgur.com/xnr0JvF.png

https://i.imgur.com/MH7OoU4.png

https://i.imgur.com/4Qrfq7q.png

I figured out a solution that leaves me enough room in the small, square greenhouse I had to build in the corner of the small lot I used (20X20).
By keeping only one square of the floor intact right in the corner next to the fence, I can remove the rest of the floor and attach both sets of stairs to that in a 90 degree angle (or have both sets in a straight line).