Agree with SST - no need to measure with a micrometer if you're gonna cut with a chain saw...

No visible warps in the building surface works for me - I use 5/8 x 12" veneered particle board shelves with 1/4 inch bulletin board cork contact cemented on the building side... Cheap and effective! They have remained dimensionally stable and flat for over 15 years (stored indoors). Made two 6' long boards for wing and fus construction, one 2 ft long for stabs and one 12" x 12" for vertical fins and rudders... allows me to move the assmbly to elsewhere while working on the next assembly....

HTH

Jim