SCARM can print 1:1. The entire layout or just a section. You need to use 2 pieces of paper at least in 8.5 x 11 on a home printer. Then cut out and tape together for one curve.
O track is named by the diameter of a circle for the curves and segments of curves for the sectional pieces and switches.
If you provide the dimensions of the area that you want to use, we can put together the plan for you. The software is much easier than making templates.
The Atlas O should work well for your climate. It's nickel-silver rail and the plastic for ties has been used on outdoor layouts in harsher climates.
You can actually do it with some string, two nails (landscape tie nail or a gutter nail) and a tape measure.
Place a nail for the center of one of the figure 8's Loop the string around it. Now pull the string to where you want the outside of the figure 8. Wrap the string around the second nail. Now scribe a circle in the ground using the second nail.
measure the length of the string from nail head to nail head. The is the radius of the circle. 2r=Diameter= O track curve size that will fit.
You are looking at 15 switches and 2 crosses plus track . I don't think you want that many switches outside. The switch motors are the weak links. You can go over/under figure 8's and manual switches to cut the switch count and cost. The over/unders are attractive for a garden railway.
Search outdoor layouts on the forum or the web and also garden layouts for ideas and videos.
if I can find the links, I'll post them for a few of my favorite outdoor layouts.
Let us know what you need. Oh, almost forgot, WELCOME to the OGR Forum!