First of all, you need to develop a blueprint for the bike. It is better to check existing drawings made by amateurs and craftsmen on the Internet. If not, you always have the option to draw your own.
Once you captured a suitable drawing, review it carefully. Move on to the next phase i.e. you need to manufacture metal tubing frame with different diameters. Purchase a suitable material and start to implement each element separately. Join elements together with the help of welding.
For the manufacture of plug you need Compactors' installation of small size and gas welding. You can use the forge and tools designed for metal forging. When the frame and fork are almost ready, you will need to drill holes for the leading "stars" in the frame and wheel attachment to the frame and fork. The holes should be perpendicular to the longitudinal axis of the frame and are parallel to each other.
Then you need to make wheel removal, leather saddle with seat post and pedals. Fasten all the details to the frame, hang the chain mechanism, wheels and brakes.