Interesting idea
It might be ok, depending on how many rats you have
but people find that homemade cages often are only ok for a short time, are often difficult to clean, and then need to be discarded because of smell etc, and then they buy a good, huge rat cage - so it is usually less expensive to just buy a good cage for rats (like a double critter nation)
Wood will absorb urine, can be chewed and often will start to stink
The cage is looks like metal hardware cloth was used - make sure this is attached to the outside and that there are no sharp edges as it will injure your rats.
I do not see any door in the cage - huge doors that give access to all levels are important for ease of cleaning as well as to put in large items
The frame needs to be powder coated (paint is baked on) or have a pet safe paint on it (there is only one type of paint that I am aware is pet safe …… galvanized metal will rust
It would be a good idea to find pans that will fit each entire level - which means huge doors so they can be removed for cleaning
Rats love hammocks so you will need to figure out how you will hang them - will the gaps in the wire you use be large enough and strong enough for hanging hammocks and handling the weight