I am still planning / collecting stage.. only build one Ron Reil burner so far.. and made one batch of the sodium silicates and few bags of perlite as insulator...(or you can use kale wool aka ceramic fiber), firebricks ... collected 0 crucible..... I guess for a forge you don't needed it... Share some pics if you are building it... still interested, just in the back burner.
I think the Ron Reil burner design is the most popular, and easiest to build... I used .025 mig welding tip 1/4 pipes 2" to 3/4 bell shape reducer and a needle valve regulator.
https://www.abana.org/ronreil/design1.shtml
If you are looking for electric oven build there is a guy here that made a post about 2 or 3 years ago.... made that out of fire bricks and an industrial temp controller and hand wound nickle chromium wires . I forgot the post, don't think have seen him post anything lately........
If you are looking for a home build coal forge, I think the kingoframdom have one that is out of a 5 gallon metal bucket and sodium silicate and perlite, he later upgrade it to use kale wool and ron reil style propane burner.
Few here I think also made the forge out of some HF portable air tanks (the steel ones) and propane burner...
and there are Induction Heaters if you have the $$$.... needs a 240V 50 amp breaker