This house is suitable for exterior and interior use. For interior use you don't need much a part of cutting and assembling it.
However, for the exterior, I advise you to treat the object with varnish.
Varnish (marine or other type) is a great tool to make your object resistant to humidity or insects and give it a nice finish.
Also, after assembling the object, it will glue it together and fill in small cracks.
Wood stain/finish can provide additional protection and a nice finish to your object. You can choose different types and colors.
Apply varnish and wood stain with a brush. Don’t forget to wash it really good after each use.
Preferably transparent. Multiple uses - you can use it to fix the leg protections so the water wont enter between the cracks. Or to fill some small holes that you’ll find.
Cord & metal tent pegs
At the bottom of the house's ribs you can find set of 3mm holes.
If necessary, you can use them to fix the house to the ground using a cord and metal tent pegs.
Cork sheet/roll or insulation board
Depending on where you live, there’s a possibility that you will want to protect cats from the cold weather. There are multiple options, for extreme cold you could install rigid insulation boards or cork sheets (2 or more mm)
Both are very easy to cut with scissors or cutter (cork even with laser cutter).
3D printer + 3D printed leg protection
If you want to use this object in exterior you need to protect its wooden legs against the humidity. One of the options is to print leg protection on a 3D printer.
This option can be useful also if you want to protect your floor. It is possible that the print will still be sharp so you will have to sand it on the edges.
You need to cut the planks into the pieces using a laser cutter with working area min. 80x50cm (31.5 x 19.7 inch).
You can get an access to this machines in various places - fablabs, makerspaces, hackerspaces or commercial services like TechShop or others.
Map of fablabs: https://www.fablabs.io/labs/map
Map of fablabs and other labs: http://www.makery.info/en/map-labs/
Map of makerspaces: http://themakermap.com/
There’s much more, not all of the places are listed in all maps, you can also try to research it by yourself.
This are the pieces you should cut on laser cutter. Consider using wood stain and first layer of varnish before the assembly