Yes but Plus Rooms are just another package dealer with all the design up front.
The point is you need to
1. Think about what you want - your wants/needs
2. Get an expert to see if it will work in CONJUNCTION with an Architect (good for spacial design) AND and engineer (will it stand up, where will the beams and columns be?)
Our problem, and those with the packages deals is that they want the design finished for them to get the engineer to look at. But its catch 22 because you don't know the best design without knowing if it will stand up or you can afford it.
After all I could say I want an completely glazed rear & side extension and no beams showing below the ceiling. That might cost a fortune, and be outside my budget, but that fact only comes up when I have paid for all the design & structural work. So, naturally, I change my mind, and hey-presto the package dealer charges another fee.
That's why you should avoid them and go to an architect & engineer (and I should have been wiser). You may pay for extra time, but at least its at your control.
(PS : I do not work for a package dealer, an architect or an engineer)