Be careful of supposed plug and play formulas for DIY roasters, especially for fluid bed roasters. It is nigh upon impossible to control for enough variables in a home setting for them to be useful. For example: It is quite possible to do 350 grams with a lowly 1kw heating element, however it seems most people use 1.5-2kw elements for roast capacities of around 400-500 grams. I personally have used both a 1.6kw and a 2kw heating element... the 1.6kw was perfect as far as responsiveness and heating curves went, but wasn't able to do a full pound of very dense beans. 2kw had plenty of power, but had a relatively small sweet spot and I ended up thrashing my SSR more than I'd like to maintain temps toward the end of the roast.
The devil is in two details: airflow and insulation. The big reason I couldn't do a pound of dense beans with the 1.6kw element is mostly because I needed such high airflow to loft the beans the heating element couldn't keep up. If I had a better funnel design I might have been able to loft those same beans with less airflow and still been able to use the smaller heating element. Insulation is also huge. Remember your heat source is the heated air you're pushing through, and any holes or conductive areas will dramatically reduce the heat capacity of that air and force you to oversize or overwork your heating element. There are plenty of easy to use insulation products that can help here, from flue tape to cut up fire blankets (make sure you're not cutting fiberglass insulation though) to HVAC insulation and beyond. Make sure you're using the proper metal alloys as well... i.e. use aluminum inside the roaster, but food grade steel for the outsides and structure. Also don't forget that air itself is one of the best and handiest insulators around... I double chambered my heating element (an inner ceramic cylinder that housed the element with an outer steel cylinder, just a couple mm of air separating them) and that made more of a difference than any other single modification I could have done. I reduced my power needs by roughly 200 watts.
Last but not least, remember that when you are dealing with cheaper heating elements the QC will not be great. I've ordered several heat gun heating elements and even whole heatguns that I've disassembled... the wattage is as advertised only about 50% of the time and often off by more than 100 watts. You definitely get what you pay for. If ordering from alibaba or aliexpress always get 3 of a kind for this same reason, and always ask for pre-shipping QC photos.