Measure the window or railing space where the flower box will sit
Choose a box size that fits the space and plant needs
Select weather-resistant wood, plastic, metal, or composite material
Gather tools such as a saw, drill, screws, measuring tape, sandpaper, and a pencil
Cut the front, back, sides, and bottom pieces to size
Sand all edges and surfaces smooth
Drill drainage holes in the bottom
Assemble the side pieces to the front and back pieces with screws
Attach the bottom piece securely
Add corner supports or brackets if needed for strength
Seal or paint the box with outdoor-safe finish
Let the finish dry completely
Line the inside with landscape fabric if desired
Add a layer of gravel or small stones for drainage
Fill the box with potting soil
Plant flowers or insert nursery pots
Water the plants thoroughly
Place the flower box in its final location
Secure it to a railing, wall, or window ledge if needed
Check drainage and watering regularly