If you don't know what a rocket stove is, have a look at "rocketstoves.com" or search at Youtube where there are tons of very good videos to get inspiration from.
Step 1: Material List
1x oval bucket with lid
1x stove-pipe 120mm x 1 m
1x stove-pipe 130mm x 50 cm
10l hydro clay for hydroculture-plants
2,5 kg chamotte mortar
Everything costs about 35 EUR
bucket (for mixing the mortar)
bucket with the same shape as the bucket for the stove but slightly smaller
Step 2: Mark the Holes
Step 3: Cut out the holes
Step 4: Insert the pipes into the holes
Step 5: Make the bottom of the stove
Mix the mortar with water so it has the consistency of ketchup. Fill the bottom of the bucket with hydroclay ( about 2 cm high) and then pour the clay pearls into the mortar. Mix it well and pour it back into the bucket.
Step 6: Make the stove-walls
Again, mix mortar and clay pearls. Then insert it into the stove and fill the gap between the outer bucket wall and the inner bucket with the mortar-clay-pearl mix. Compress the clay-pearls with a stick to prevent air bubbles in the wall. Let the mortar sit for at least 24h.