What I am asking is to make it HO it needs to be reduced by the % you gave and your math works out pretty well. So how much would it have to be blown up for garden scale and look resonable based on a 7 foot door.
If I understand you correctly, then it is very simple math.
It is just (87/24) x 44.6% = 161.7% (approx.) to scale the D.E. Main Street Station to 1/24th scale. As noted, every D.E. paper model is different and needs a different scale factor.
Most of the D.E. and the Haunted Dimension models start at larger than HO scale so one ends up scaling down and all the parts fit on a sheet of paper. When Scaling up, you either need a bigger piece of paper or you have to figure out how to break up the pieces onto two pieces of paper.
BTW, my favorite paper for paper models is some form of ink jet "Matte Paper Heavyweight" as it will do a good job of absorbing the inks, is thick enough to stand up, and has a dull (matte) finish. If I want something "shiny" like painted wood or metal then I would use a glossy paper which is pretty thick as well.
For these models in "HO" heavyweight inkjet paper is probably thick enough and you don't need to go all the way to card stock. This is of course for making HO scale models where the parts are small. As you scale up, you will may need a thicker/sturdier paper/card-stock (or at least some backing for any large sections).