For a start, put some sketches onto your house floor plans.
Break them into different trades like wet works, electrical works, air con, grille works, landscape work, etc

Look around for reno contractors. Get them to quote you and then analyses their quotations. Take you time in selecting one as you will be surprise with the quote you will receive. Some can be sky high High price does not meant better quality and also lower price does not mean bad quality

doubt it will cost that much... unless it include the ID fees and also commission

If you go for clay roof tiles, the roof tile profile should be the same as the adjoining existing roof tiles. The roof pitch should also match. You will have to check if by matching the existing roof pitch, will it look nice and have enough headroom?
Alternative, you could raise (adjust) the pitch of the existing roof. But then, have to check if the adjusted pitch would be sufficient?

Clay tiles would be cooler as compered to the RC roof. BTW, most developers does not provide you with clay roof tiles. They only use concrete roof tiles which are way cheaper.
Concrete roof tiles are different from clay roof tiles

You should be able to easily distinguish between the clay roof tiles with concrete roof tiles. The underneath of the clay roofing tiles will be clay in colour. Some manufacturer apply a layer of coating on the top to give a shining effect. They could be any colour.
Wile the underneath of the concrete roofing tile will be the cement colour

Concrete roof tiles should be around RM1/pc. Not sure of the current price for the clay roof tiles. When I bought some clay tiles, (That was about 8 years ago) I paid about RM2.8/pc