My son his as big of a leGo fan as i was and still am. Used a couple packs of foam tiles 24″  x 24″ 3/8 thick and a roll of 1/4 thick 4ft x 8 ft mat, for the flexible parts save uva foam but 1/8 thick 8″ x10″ lots of paint 3 cans of golden spray paint, latex colored paint from dollar store 100ml bottle @ 1,25$, the eye part is made with a small piece of window screen, and got paited whole. 100$ total

All held together with hot glue, electrical tape works wonders holding the pieces while the glue sets. Plan ahead it goes quick about 40 sticks used the big ones.

Uva foam is easy to shape, paint, loves hot glue, best of all cheap as hell.

Keep in mind, that if you don t prime the foam it will soak up more paint, primer was more expensive  then the gold paint, but if you have it available, it will yeild a nicer finish.

The foam tiles come with a checker plate finish, obviously that is on the inside.

Mesure your child for rough scaling. In my case my son is 48″ tall, so the 24 inch tiles worked out great, i made modification in order to be a semi fonctionnal costume, ie elbow joints and knee joints.

A sharp utility knife carves that thing like butter, get disposable blades, dont break them off, reuse them later, the sharper the better, some gaps were filled with latex caulk, prior to painting.

The tile color is irrelevant. Because of finishing. Mine were avalable in black and grey, perfect for a batman costume, no paint would have been needed, only realised it after the head was made.

The whole costume took a couple day to shape, another couple to finish, i believe a lego batman suit would take half the time, or any other if the foam color is the same as your minifig model…my son loves it…too bad its still august…maybe i ll build the dragon for myself.