Requires Bob's Function Library: https://mods.factorio.com/mods/Bobingabout/boblibrary

This mod allows the player to build various things that normally spawn in the map. Most of these are only decorative plants, but some solid structures and even alien spawners can be crafted!

There's a file in the mod called config.lua, in which you can enable/disable crafting for plants and alien spawners.

Complete list of stuff this mod adds:
+5 new technologies: Environmental Decor, Environmental Decor 2, Environmental Decor - Grasses, Environmental Objects, and Alien Spawning
+2 craft-able alien buildings: Biter spawner and Spitter spawner
+1 new crafting material, Foliage
+Crafting recipes and items for the following decorative objects:
-Stone Boulder
-Dead Grey Tree Trunk
-Dead Dry Hairy Tree Trunk
-Dead Tree Trunk
-Brown, Green, and Red Asterisks
-Green Pita
-Mini Green Pita
-Mini Green, Brown, and Orange Corals
-Brown Fluff
-Dry Brown Fluff
-Garballo
-Mini Dry Garballo
-Mini Green Bush
-Small Green Grass
-Brown Carpet Grass
-Brown Hairy Grass
-Brown Cane & Brown Cane Cluster
-Green Hairy Grass
-Green Carpet Grass
-Ship Wreck Grass
-Red Desert Bush
-Small Rock
-Red Desert Rocks