I made one for our Leopard, was VERY easy.
a sheet of MDF, IIRC it was 3/4" and was a standard sheet size in B&Q, cant remember exact but was probably 1.5M longish by 80cm or so (dont quote me!)
then each sidewall was butt jointed, 2 planks high of pine square planed. Screwed from the underside.
this made a substantially strong and big table.
then a mount for the heat lamp, this was essentially an upside down L, metal L bracket, and a screw with big washer for the lamp end.
i did have a shelter area, but it wasnt really used so removed it.
Also used B&Q sticky floor tiles for the base and walls to make it easier to keep clean.
this lasted a number of years till he outgrew the table and is now outside in a heated shed (32 degree under his lamp, ambient in the rest of the area is no les than 25!) , with a large outside run.
I then affixed 4 legs (3x2" wood) to each corner and was a workbench/table in the cellar for another few years, rock solid and stable as anything.
there was plenty of water and suchlike spilt, no real damage to the wood apart from discoloration after the years.
worked perfect for the needs.
also if you go this route i would get 4 handles and attach them to the sides for easier movement, it was big and heavy!
i cant find any pictures, but if you want me to hunt, i will try toi dig some out tomorrow.